The four of us have come together, now joined by many others, to support a global effort to reduce reliance on nuclear weapons, to prevent their spread into potentially dangerous hands, and ultimately to end them as a threat to the world. We do so in recognition of a clear and threatening development.

The accelerating spread of nuclear weapons, nuclear know-how, and nuclear material has brought us to a tipping point. We face a very real possibility that the deadliest weapons ever invented could fall into dangerous hands.

But as we work to reduce nuclear weaponry and to realize the vision of a world without nuclear weapons, we recognize the necessity to maintain the safety, security and reliability of our own weapons. They need to be safe so they do not detonate unintentionally; secure so they cannot be used by an unauthorized party; and reliable so they can continue to provide the deterrent we need so long as other countries have these weapons. This is a solemn responsibility, given the extreme consequences of potential failure on any one of these counts.

For the past 15 years these tasks have been successfully performed by the engineers and scientists at the nation's nuclear-weapons production plants and at the three national laboratories (Lawrence Livermore in California, Los Alamos in New Mexico, and Sandia in New Mexico and California). Teams of gifted people, using increasingly powerful and sophisticated equipment, have produced methods of certifying that the stockpile meets the required high standards. The work of these scientists has enabled the secretary of defense and the secretary of energy to certify the safety, security and the reliability of the U.S. nuclear stockpile every year since the certification program was initiated in 1995.

The three labs in particular should be applauded for the success they have achieved in extending the life of existing weapons. Their work has led to important advances in the scientific understanding of nuclear explosions and obviated the need for underground nuclear explosive tests.

Yet there are potential problems ahead, as identified by the Strategic Posture Commission led by former Defense Secretaries Perry and James R. Schlesinger. This commission, which submitted its report to Congress last year, calls for significant investments in a repaired and modernized nuclear weapons infrastructure and added resources for the three national laboratories.

These investments are urgently needed to undo the adverse consequences of deep reductions over the past five years in the laboratories' budgets for the science, technology and engineering programs that support and underwrite the nation's nuclear deterrent. The United States must continue to attract, develop and retain the outstanding scientists, engineers, designers and technicians we will need to maintain our nuclear arsenal, whatever its size, for as long as the nation's security requires it.

This scientific capability is equally important to the long-term goal of achieving and maintaining a world free of nuclear weapons—with all the attendant expertise on verification, detection, prevention and enforcement that is required.

Our recommendations for maintaining a safe, secure and reliable nuclear arsenal are consistent with the findings of a recently completed technical study commissioned by the National Nuclear Security Administration in the Department of Energy. This study was performed by JASON, an independent defense advisory group of senior scientists who had full access to the pertinent classified information.

The JASON study found that the "[l]ifetimes of today's nuclear warheads could be extended for decades, with no anticipated loss in confidence, by using approaches similar to those employed in Life Extension Programs to date." But the JASON scientists also expressed concern that "[a]ll options for extending the life of the nuclear weapons stockpile rely on the continuing maintenance and renewal of expertise and capabilities in science, technology, engineering, and production unique to the nuclear weapons program." The study team said it was "concerned that this expertise is threatened by lack of program stability, perceived lack of mission importance, and degradation of the work environment."

These concerns can and must be addressed by providing adequate and stable funding for the program. Maintaining high confidence in our nuclear arsenal is critical as the number of these weapons goes down. It is also consistent with and necessary for U.S. leadership in nonproliferation, risk reduction, and arms reduction goals.

By providing for the long-term investments required, we also strengthen trust and confidence in our technical capabilities to take the essential steps needed to reduce nuclear dangers throughout the globe. These steps include preventing proliferation and preventing nuclear weapons or weapons-usable material from getting into dangerous hands.

If we are to succeed in avoiding these dangers, increased international cooperation is vital. As we work to build this cooperation, our friends and allies, as well as our adversaries, will take note of our own actions in the nuclear arena. Providing for this nation's defense will always take precedence over all other priorities.

Departures from our existing stewardship strategies should be taken when they are essential to maintain a safe, secure and effective deterrent. But as our colleague Bill Perry noted in his preface to America's Strategic Posture report, we must "move in two parallel paths—one path which reduces nuclear dangers by maintaining our deterrence, and the other which reduces nuclear dangers through arms control and international programs to prevent proliferation." Given today's threats of nuclear proliferation and nuclear terrorism, these are not mutually exclusive imperatives. To protect our nation's security, we must succeed in both.

Beyond our concern about our own stockpile, we have a deep security interest in ensuring that all nuclear weapons everywhere are resistant to accidental detonation and to detonation by terrorists or other unauthorized users. We should seek a dialogue with other states that possess nuclear weapons and share our safety and security concepts and technologies consistent with our own national security.

Mr. Shultz was secretary of state from 1982 to 1989. Mr. Perry was secretary of defense from 1994 to 1997. Mr. Kissinger was secretary of state from 1973 to 1977. Mr. Nunn is former chairman of the Senate Armed Services Committee.