Leaders or representatives from 47 countries recently attended the nuclear security summit in Washington. By holding a bilateral meeting with U.S. President Barack Obama and delivering an important speech at the summit, Hu Jintao highlighted China's positive image for people across the globe and helped reverse the deterioration of US-China relations.

Obviously, it takes a long path toward establishing a global mechanism to counter nuclear proliferation and nuclear terrorism. Many of these leaders were not quite sure whether they would come away from the summit empty-handed.

However, they decided to attend the summit mainly to respond positively to Obama, who had launched a number of initiatives to build a nuclear-free world. The same is true for Hu Jintao and his decision to attend the summit.

Hu's visit to Washington will help lead the bilateral relations toward a positive direction. Although some disputes continue between the two countries, Hu's visit to Washington will no doubt contribute to lowering U.S. hostility toward China.

Earlier, the rapid increase in GDP had stimulated some Chinese diplomats to take blind pride in dealing with their foreign counterparts. Now, it is time to rethink whether it is necessary to adhere to the well-established principle of keeping a low profile in handling Sino-American relations.

China's GDP will soon become the second largest in the world. Who is the greatest beneficiary from the pursuance of this principle over the past three decades? Needless to say, it is China.

Now, China is just halfway through its course of "peaceful rise." In the foreseeable future, the United States will remain the No. 1 power in the world. Two decades from now, who will become the greatest beneficiary if China, as the biggest developing country, is able to maintain stable relations with Washington? Obviously, the answer is China.

In his opening statement at the summit, Obama pointed out that in today's world, the world has reduced the risk of a nuclear war between big powers, but the threat of nuclear terrorist assaults is increasing. He is right. Terrorists can penetrate all places throughout the world without leaving a trace.

It is difficult for all major powers, especially the United States, to detect and prevent them from launching assaults including sudden attacks with "dirty bombs" as weapons. As such, the whole world faces the most serious security challenge.

Such a strategic assessment prompted Obama to convene the nuclear security summit as well as his earlier initiative of "a world free of nuclear weapons." Preoccupied by this assessment, he has spared no effort to promote the campaign of countering nuclear proliferation and nuclear terrorism.

To fight nuclear terrorism, the summit focused on establishing an international nuclear security mechanism. The United States and many countries face the threat of nuclear terrorism. China is no exception.

In case the East Turkistan separatists consider the timing is mature to intensify conflicts with Beijing, they will no doubt take whatever means necessary to penetrate nuclear facilities or acquire "dirty bombs." Moreover, the large-scale construction of nuclear power plants in China introduces more security challenges. China will be in the peak period of building such plants in the next two decades.

The ongoing construction of such plants scattered in coastal areas would expose the nation to threat. A terrorist attack on even one plant would result in consequences more serious than that of detonating a nuclear bomb over a city. Taking this into account, Beijing has adopted various measures to strengthen nuclear security in recent years.

As a positive response from China to the international community, Hu Jintao made the decision to attend the summit, which reflects that Beijing and Washington actually are sharing common interests by making joint efforts to establish a global mechanism for countering nuclear proliferation and nuclear terrorism.

This action indicates that Beijing regards nuclear terrorist assaults as a huge threat to national security interests and it hopes to strengthen international cooperation to limit or even eliminate this type of threat.

Also, this decision has indeed enabled China to avert a head-on collision with the United States and helped reverse a deterioration of U.S.-China relations. Based on this, we can suppose that Beijing is able to conduct strategic adjustment at a critical moment and formulate appropriate foreign policies.

The release last week of the Obama administration's Nuclear Posture Review brings long overdue attention to the vital issue of U.S. strategic posture. Issues raised in the NPR and START have reinvigorated a crucial national nuclear dialogue that has been missing.

As the chairman and vice chairman of Congress's bipartisan Strategic Posture Commission, which issued its report last May, we have watched with great interest the administration's steady progress this past year on its Nuclear Posture Review and the START negotiations.

Themes from our report run through the Nuclear Posture Review and are embodied in the new START agreement. While debate and disagreement must be part of the crossfire in this renewed nuclear dialogue, we want to emphasize important dimensions of both the Posture Review and START treaty that figure prominently in our bipartisan report.

Now that the NPR is completed, we see that it is compatible with our recommendations. The review gives a comprehensive and pragmatic plan for reducing nuclear risks to the United States. We believe it offers a bipartisan path forward - while allowing for healthy disagreements on specific issues.

And it incorporates many of our points - such as pursuing a quick and modest reduction of nuclear weapons with Russia and sustaining the nuclear triad of land-based ICBMs, sea-based SLBMs and bombers. It also recognizes that nuclear weapons safeguarded U.S. security during the Cold War by deterring attack and that we will need them for deterrence in the foreseeable future, as long as others also possess them.

We also see that the NPR puts special emphasis, as our report recommended, on improving the nation's complex nuclear infrastructure and enhancing programs to recruit and keep the nation's best scientific minds. The administration's commitment to increase investment in our national laboratories also ensures that they continue their important role in sustaining a safe, secure and effective nuclear arsenal and in solving many other problems facing the nation.

The review is correct to make preventing nuclear terrorism and proliferation the top priority, while also seeking to strengthen deterrence and to reassure U.S. allies and recognizing the importance of strategic stability with Russia and an emerging China. Our commission reached the same conclusions.

The NPR's changes in U.S. declaratory policy - especially the assurance that Washington "will not use or threaten to use nuclear weapons against non-nuclear parties to the Nonproliferation Treaty that are in compliance with their nuclear nonproliferation obligations" - go beyond our recommendation that the U.S. retain "calculated ambiguity."

It is, however, a sensible variation on a theme that the U.S. should support nonproliferation while preserving deterrence for itself and its allies.

We also note that the NPR chose, as we advised, to avoid adopting a "no first use" policy for nuclear weapons while narrowing the scope of possible first use to "extreme circumstances" - language that was in our bipartisan report.

We believe that the substantial edge the U.S. has developed in conventional military capabilities, which the NPR notes, permits this country to sharply reduce reliance on nuclear weapons. But we caution those who make light of this major U.S. strategic advantage and its implications.

We support the NPR's call for the U.S. not to develop new nuclear weapons now. Our report similarly called for a case-by-case approach to extending the life of today's warheads. And we agree that the focus should be on safety, security and reliability - not developing new military capabilities.

The NPR echoes our call to negotiate a worldwide end to the production of new fissile materials - the key ingredients of nuclear weapons.

Our final report strongly endorsed the U.S. deterrence policy to cover our allies and partners with the U.S. nuclear umbrella - an objective the NPR also embraces.

The report suggested deploying proven missile defenses against threats such as North Korea and Iran but emphasized, as the NPR does, that these defenses should not be so big as to encourage Russia to add warheads to counter them, which would only undermine efforts to reduce nuclear weapons. We included China as well as Russia in this.

But in two areas, we believe the NPR might have fallen short of the mark.

First, we understand that the review considered declassifying additional information about the size and composition of the U.S. nuclear stockpile. It should have done so. This would demonstrate U.S. leadership on the transparency that is needed to secure nuclear materials globally and to bolster strategic stability with Russia and China.

Second, the NPR called for the consideration of conventional "prompt global strike" capabilities. But it did not explain whether these systems would have a niche role against small regional powers such as North Korea or be an ultimate substitute for nuclear weapons in deterrence with Russia and China.

We feel the former is the only sensible approach. Keeping this issue ill-defined creates needless anxiety in Moscow and Beijing that could lead to future problems.

Even with these two caveats, the 2010 Nuclear Posture Review makes important strides in charting a sustainable bipartisan path forward for the United States.

Healthy disagreement over some NPR specifics should not obscure the valuable contribution it makes to advancing U.S. security interests - resting, as it does in part, on our bipartisan 2009 Strategic Posture Commission report.

William J. Perry served as secretary of defense in the Clinton administration. He was chairman of the Congressional Commission on the Strategic Posture of the United States. James R. Schlesinger was the nation's first energy secretary and served as secretary of defense from July 1973 to November 1975. He was vice chairman of the Congressional Commission on the Strategic Posture of the United States.

THIS has been a remarkable time for the Obama administration. After a year of intense internal debate, it issued a new nuclear strategy. And after a year of intense negotiations with the Russians, President Obama signed the New Start treaty with President Dmitri Medvedev in Prague. On Monday, the president will host the leaders of more than 40 nations in a nuclear security summit meeting whose goal is to find ways of gaining control of the loose fissile material around the globe.

New Start is the first tangible product of the administration's promise to "press the reset button" on United States-Russian relations. The new treaty is welcome. But as a disarmament measure, it is a modest step, entailing a reduction of only 30 percent from the former limit - and some of that reduction is accomplished by the way the warheads are counted, not by their destruction. Perhaps the treaty's greatest accomplishment is that the negotiations leading up to its signing re-engaged Americans and Russians in a serious discussion of how to reduce nuclear dangers.

So what should come next? We look forward to a follow-on treaty that builds on the success of the previous Start treaties and leads to significantly greater arms reductions - including reductions in tactical nuclear weapons and reductions that require weapons be dismantled and not simply put in reserve.

But our discussions with Russian colleagues, including senior government officials, suggest that such a next step would be very difficult for them. Part of the reason for their reluctance to accept further reductions is that Russia considers itself to be encircled by hostile forces in Europe and in Asia. Another part results from the significant asymmetry between United States and Russian conventional military forces. For these reasons, we believe that the next round of negotiations with Russia should not focus solely on nuclear disarmament issues. These talks should encompass missile defense, Russia's relations with NATO, the Conventional Armed Forces in Europe Treaty, the Intermediate-Range Nuclear Forces Treaty, North Korea, Iran and Asian security issues.

Let's begin with missile defense. Future arms talks should make a serious exploration of a joint United States-Russia program that would provide a bulwark against Iranian missiles. We should also consider situating parts of the joint system in Russia, which in many ways offers an ideal strategic location for these defenses. Such an effort would not only improve our security, it would also further cooperation in dealing with the Iranian nuclear threat, including the imposition of consequential sanctions when appropriate.

NATO is a similarly complicated issue. After the cold war ended, Russia was invited to NATO meetings with the idea that the country would eventually become an integral part of European security discussions. The idea was good, but the execution failed. NATO has acted as if Russia's role is that of an observer with no say in decisions; Russia has acted as if it should have veto power.

Neither outlook is viable. But if NATO moves from consensus decisions to super-majority decisions in its governing structure, as has been considered, it would be possible to include Russia's vote as an effective way of resolving European security issues of common interest.

The Russians are also eager to revisit the two landmark cold war treaties. The Conventional Armed Forces in Europe Treaty enabled NATO and Warsaw Pact nations to make significant reductions in conventional armaments and to limit conventional deployments. Today, there is still a need for limiting conventional arms, but the features of that treaty pertaining to the old Warsaw Pact are clearly outdated. Making those provisions relevant to today's world should be a goal of new talks

Similarly, the 1987 treaty that eliminated American and Soviet intermediate-range ballistic missiles was a crucially important pact that helped to defuse cold war tensions. But today Russia has neighbors that have such missiles directed at its borders; for understandable reasons, it wants to renegotiate aspects of this treaty.

Future arms reductions with Russia are eminently possible. But they are unlikely to be achieved unless the United States is willing to address points of Russian concern. Given all that is at stake, we believe comprehensive discussions are a necessity as we work our way toward ever more significant nuclear disarmament.

William J. Perry, a senior fellow at the Freeman Spogli Institute for International Studies, was the secretary of defense from 1994 to 1997. George P. Shultz, the secretary of state from 1982 to 1989, is a distinguished fellow at the Hoover Institution.

Hendrik Hertzberg writes that the end of the Cold War and the coming of global warming have brought about increased support for nuclear power, even among some environmentalists (The Talk of the Town, March 22nd). But many of us who work on nuclear-proliferation issues are dismayed by the growth of nuclear energy. Expanded nuclear power in industrial countries will inevitably mean expanded nuclear exports to less developed countries as manufacturers try to recoup their investments in a limited domestic market by selling abroad. It can be shown statistically that countries that receive nuclear assistance are more likely to build nuclear weapons, especially when they perceive threats to their security. India, Pakistan, and Israel started their nuclear programs with the importation of research reactors carrying peaceful-use requirements; with help from other countries, they were able to then realize their desire for weapons. Iran appears to be heading in the same direction. Given the documented interest in nuclear materials of terrorist organizations like Al Qaeda, and given the questionable assumptions that nuclear-energy economics is fraught with, it makes little sense to push nuclear power at a time when protections against proliferation are still so problematic. Improved energy efficiency is a safer, greener, and cheaper alternative.

With an April 8 date set for the United States and Russia to sign a new nuclear arms reduction treaty, each country is preparing to cut their deployed weapons by about 30 percent. That caps each side at 1,550 nuclear warheads and bombs and 700 deployed strategic missiles and bombers.

The pact, which needs approval by the U.S. Senate and Russian Duma, is the culmination of a year's worth of often tumultuous negotiations. It's also an important step in President Obama's push for a nuclear-free world, an idea that was given a roadmap during a 2006 conference at Stanford's Hoover Institution. The conference, which was convened by former Secretary of State George Shultz and Stanford physicist Sidney Drell, resulted in a Wall Street Journal op-ed in January 2007 calling for a world without nuclear weapons.

The piece was written by Shultz, a professor emeritus at Stanford's Graduate School of Business and a distinguished Hoover fellow; William Perry, President Clinton's defense secretary and an emeritus senior fellow at Stanford's Freeman Spogli Institute for International Studies; Henry Kissinger, who served as secretary of state in the Nixon and Ford administrations; and Sam Nunn, a former chairman of the Senate Armed Services Committee and CEO of the Nuclear Threat Initiative.

President Obama mentioned the four men in a March 26 statement announcing the new treaty, noting their support for more assertive action in reducing nuclear weapons.

David Holloway, a professor of international history and faculty member at FSI's Center for International Security and Cooperation, participated in the Hoover conference and has analyzed the steps taken to shrink the world's nuclear stockpile.

Holloway, author of Stalin and the Bomb: The Soviet Union and Atomic Energy, 1939-1956, spoke with the Stanford News Service about the latest pact between the United States and Russia, and what the prospects are for further reduction of nuclear weapons.

Put the treaty in context. How significant is it?

You could say it's a small step in an important process. In the 1980s, there were about 70,000 nuclear weapons in the world. Most were owned by the U.S. and the Soviet Union. Now there are about 22,000 nuclear weapons, 90 percent of them owned by the U.S. and Russia. A number of those weapons are slated for dismantling, but it takes time to do that. Meanwhile, the feeling is that it's better to regulate the US-Russian nuclear relationship by treaty, so that it does not develop in an unpredictable way or a way that causes instability in the relationship.

This treaty reduces only the number of deployed warheads and nuclear delivery systems. What will happen to those weapons?

Some missile sites will be closed down and the warheads will be put into storage. The treaty apparently won't commit either side to dismantling the warheads. It only moves them from deployment. But cutting the number of delivery systems is important because if you don't have the missiles or bombers to launch the warheads, then the warheads aren't much use.

Is there a system in place to keep each country in compliance with the treaty?

Each country has the capacity to monitor the other side's compliance with the treaty. There are satellites that can see what the other side is doing; there are arrangements for the electronic monitoring of test flights and so on; and there are exchanges of inspectors. The two countries have considerable experience of cooperation in this area.

The treaty does not restrict America's plans to build a missile defense shield in Europe. But explain the tensions between Russia and U.S. over that issue.

This was probably the most difficult part of the negotiations. The Russians were eager to get limits on American defenses against ballistic missiles, and the U.S. was very reluctant to include them in this treaty. The Russians are worried what the effect of defense systems would be on their ability to retaliate in the event of an American first strike - as improbable as that is.

Despite that tension, the Obama administration has said it wants to "reset" U.S.-Russian relations. Does this treaty help?

The treaty makes great sense in terms of that agenda. It's an affirmation of Russia's position as a nuclear superpower, and it gives the Russians some assurance that they will maintain the status of an American partner in this area.

What the United States wants is help on issues like Iran and Afghanistan: making sure we can get supplies across Russia to Afghanistan and persuading Russia to continue putting pressure on Iran to back away from making nuclear weapons.

The treaty will have to be ratified by the U.S. Senate. How do you expect that to play out?

The mood in Washington isn't very bipartisan at present, of course. And there are many people who think: why should we have an agreement with the Russians? We're stronger; they're weaker. We shouldn't limit our own flexibility by negotiating agreements. That was a strong view in the Bush administration - that arms control is a bad thing and it only limits our freedom of action. And the issue of missile defense systems will be a contentious issue. There are people who want to see absolutely no restrictions on our defenses against ballistic missiles, whereas that is one of the goals of Russian policy.

How does this treaty fit in with concerns that unstable countries and terrorist groups might get their hands on nuclear weapons?

The Russians aren't about to blow us up, and we're not about to blow them up. The real fear is that other people will get hold of nuclear weapons. In the Obama administration's view, this treaty is part of a single effort to create a tough nuclear regime where states that have nuclear weapons are taking steps toward getting rid of them. And at the same time, the mechanisms for preventing new states - and in particular terrorist groups - from getting hold of nuclear weapons or the materials to make them are being strengthened.

Under the nuclear nonproliferation treaty, which entered into force in 1970, states that have nuclear weapons are obliged to pursue nuclear disarmament, while the states without them have promised not to acquire them. So if you want to strengthen this nuclear regime and make it harder for other states and terrorist groups to get nuclear weapons, then those with the nuclear weapons need to be moving toward zero. That's a key element in the administration's policy. The judgment is that a discriminatory regime is not viable in the long run.

What's the likelihood that we'll get to world free of nuclear weapons?

The president laid that out as a goal, and he said it probably wouldn't happen in his lifetime. Nobody can say that we can get to zero in say 20 years, but we do know what the first steps should be on such a path, and this treaty is one of them.

Before the world could get to zero nuclear weapons, there would have to be certainty that nobody could break out and say, "I've got lots of nuclear weapons, so you better listen to me."

The goal of zero is a vision, but I think it's an essential one because it gives you a sense of the direction you should go in.

What are the next steps Russia and the U.S. will take to reduce their nuclear stockpiles?

It's not clear. There is no agreement to have a further round of talks, but I very much hope there is one. There could be further negotiations on the reduction of strategic forces, but it seems more likely that talks might focus on the possibilities of cooperation in ballistic missile defense and/or on tactical nuclear weapons - the shorter-range systems that are not covered by the new treaty.