OVER the last three years, as I delved into the world of American nuclear weapons, I felt increasingly as though I had stepped into a time warp. Despite the nearly total rearrangement of the international security landscape since the demise of the Soviet Union in 1991, the rise of Islamic terrorism and the spread of nuclear materials and technology to volatile nations like Pakistan, North Korea and Iran, the Defense Department remains enthralled by cold war nuclear strategies and practices.

Barack Obama took office determined to change that. He has made progress on many fronts. Last week, he outlined a new, no-frills defense strategy, downsizing conventional forces. He now needs to double down on his commitment to refashion nuclear forces. He should trim the American nuclear arsenal by two-thirds to bring it down to a sensible size, order the Pentagon to scale back nuclear war-fighting plans so they are relevant to contemporary threats, remove most American intercontinental, land-based missiles from high alert and drop the quaint notion that a fleet of aging B-52 bombers can effectively deliver nuclear weapons to distant targets.

This agenda is not only desirable, it is doable without undercutting American security. It would save tens of billions of dollars a year, a relatively small amount by Pentagon standards, but every billion counts as Leon E. Panetta, the defense secretary, trims his budget. And the steps can safely be taken without requiring reciprocal moves by Russia that must be codified in a treaty.

For the last few months, the Obama administration has been conducting a classified review of the doctrines and operations that determine the shape and potential uses of America’s nuclear armaments. If the president pushes back against the defenders of the old order at the Pentagon and other redoubts of the nuclear priesthood, he can preserve American security while making the United States a more credible leader on one of today’s most critical issues — containing the spread of nuclear weapons. Like a chain smoker asking others to give up cigarettes, the United States, with its bloated arsenal, sounds hypocritical when it puts pressure on other nations to cut weapons and stop producing bomb-grade highly enriched uranium, the key ingredient of a crude nuclear weapon.

American actions alone won’t end the proliferation danger, but American leadership is essential to any hope of containing the threat.

Sam Nunn, the former chairman of the Senate Armed Services Committee, and anything but a dove over the years, rightly warns that the spread of weapons and the means to make them may soon reach a combustible stage where New York, Washington, Moscow, Tokyo or London is at risk of a nuclear terrorist attack.

Mr. Nunn and other keepers of America’s cold-war armory, George P. Shultz and Henry A. Kissinger, former Republican secretaries of state, and William J. Perry, a former Democratic defense secretary, have banded together in recent years to press, among other things, for cutting nuclear forces, de-alerting missiles and, ultimately, eliminating nuclear arms. Mr. Obama has embraced their aims and welcomed them to the Oval Office. Their high-powered, bipartisan alliance, if adroitly employed by the White House, ought to provide some political cover as Mr. Obama reshapes nuclear policy while running for a second term.

There is no national security rationale for maintaining an arsenal of some 5,000 warheads, with nearly 2,000 arms ready to use on short notice and the rest in reserve. We don’t need thousands of warheads, or even hundreds, to counter threats from countries like Iran or North Korea.

The only conceivable use of so many weapons would be a full-scale nuclear war with Russia, which has more warheads than the United States. But two decades after the collapse of the Soviet Union, even Vladimir V. Putin, with his authoritarian bent, is not about to put Russia on a collision course with the United States that leads to nuclear war. China, equally unlikely to escalate tensions to the nuclear brink, probably has fewer than 400 warheads and a policy to use them only in self-defense. Pakistan has roughly 100, North Korea fewer than 10 and Iran, so far, zero.

The United States could live quite securely with fewer than 1,500 warheads, half in reserve. Defenders of the nuclear faith claim we need 5,000 weapons as a hedge against warheads that may become defective over time. But an elaborate Energy Department program to maintain and refurbish warheads, the Stockpile Stewardship Program, has proved highly effective.

Another oft-cited reason for increasing our arsenal is that the Pentagon’s nuclear war-fighting plans still call for striking hundreds of targets in Russia and China, as well as dozens of sites in a number of other publicly unidentified nations — presumably Iran, North Korea and Syria — considered potentially hostile to the United States and eager to possess unconventional weapons.

Washington’s current nuclear war plans remain far too outsize to deal with any plausible attack on America. Mr. Obama could remove some nations from the hit list, starting with China, and tell his generals to limit the number of targets in the countries that remain.

The oversize American nuclear arsenal features an equally outdated reliance on long-distance bombers. The days when lumbering B-52 bombers could play a central role in delivering nuclear weapons — memorably spoofed in Stanley Kubrick’s “Dr. Strangelove” — ended decades ago. Mr. Obama should ground the bombers and depend on land- and sea-based missiles.

The high-alert status of America’s intercontinental ballistic missiles is another anachronism. There are few circumstances that might require the United States to quickly launch nuclear-tipped missiles, and missiles on high alert are an invitation to an accident, or impulsive action. In the first year of his presidency, Mr. Obama outlined an ambitious nuclear weapons agenda. Absent new action, Washington will remain frozen in a costly cold war posture.

Philip Taubman is a former New York Times bureau chief in Moscow and Washington and the author of “The Partnership: Five Cold Warriors and Their Quest to Ban the Bomb.”

The legacy of the late North Korean leader Kim Il Sung's decision in the early 1990s to pursue a strategic partnership with the United States has run its course. In its place, the focus of Pyongyang's policies has decisively shifted to Beijing. However wary the North Koreans may be of their neighbor, the fact is that from Pyongyang's viewpoint, the Chinese have delivered and the United States did not.

Any shards remaining from the North's previous, decades-long effort to normalize ties with the U.S. were swept away by current leader Kim Jong Il's trip in May to China, his third in barely a year. Based on our discussions with Chinese officials, we believe that during that visit, Pyongyang and Beijing came to an understanding that, in preparation for planned, major domestic political events in 2012, both sides require sustained political stability, a convergence of interests that provides the opportunity for expanding bilateral relations beyond anything enjoyed in the past. The North is building toward a "prosperous and powerful" nation in celebration of the Kim Il Sung centenary in April; the Chinese are looking toward their 18th Party Congress scheduled for late next year. In both cases, it was apparently decided, stability on the Korean peninsula would serve economic programs and the succession of a new generation of leaders.

In the arrangements — formal and informal — that emerged from Kim Jong Il's discussions with his hosts, Pyongyang agreed not to "make trouble" (as the Chinese described it to us) in the short term, presumably meaning no deliberate military provocations, no third nuclear test and no launch of another ballistic missile. Beyond that, the talks ended in a compromise that neither side found entirely satisfactory. Kim came away with less aid and a smaller Chinese commitment of support than he had sought, though Pyongyang typically asks for more than it can get.

The North did, however, receive increased access to both Chinese capital and technology in spite ofUnited Nations and other foreign sanctions. Kim also obtained, through the establishment of joint economic zones with China along the Yalu River, a locale to test adjustments necessary to economic development, adjustments that would fall short of what Beijing considers genuine economic reform. Chinese President Hu Jintao, we were told, had to settle for Kim's promise to cause less trouble but without a North Korean commitment to serious steps toward denuclearization.

We believe that this pivot toward Beijing is no routine oscillation in North Korean policy. The drive to normalize relations with the U.S. from 1991 to 2009 had been real, sustained and rooted in Kim Il Sung's deep concern about the regime's future in the aftermath of the collapse of the Soviet Union. Perhaps there was no better demonstration of the North's approach in those years than the situation on Oct. 25, 2000 — the 50th anniversary of the entry of the Chinese People's Volunteers into theKorean War. Who was in Pyongyang on that date meeting Kim Jong Il? The Chinese defense minister? No, he was cooling his heels while Kim met with the U.S. secretary of State. That was no accident of scheduling on Pyongyang's part; it would not happen again today.

If the paradigm shift is real, we expect the North in the near to medium term to make far less overt trouble. Less tension on the Korean peninsula? What could be wrong with that? Nothing, as long as it is understood that such tranquillity will also provide a veil for the North's continuing pursuit of nuclear weapons and increasingly sophisticated delivery systems. With the onset of stability and growing Chinese-North Korean cooperation, Pyongyang may well calculate that the outside world's focus on the North Korean nuclear program will become diffuse. Indeed, the North Koreans have long assumed that given enough time, the world would resign itself to their nuclear weapons, as happened with India and Pakistan.

To help things along, it isn't out of the question that Pyongyang might even agree to some U.S. efforts to contain the nuclear program through a series of what Washington calls "pre-steps." The North has repeatedly expressed willingness to consider discussion of its uranium enrichment program and moratoriums on missile and nuclear tests. As unilateral actions, these would have short-term benefits by further stabilizing the situation to provide additional room for discussions. But in the absence of long, serious negotiations between the two sides, they will turn out to be no more meaningful than the ill-considered agreements of the now moribund six-party talks.

All of which brings us back to the deepening North Korean-Chinese ties, and the downgrading in Pyongyang's calculations of relations with the United States. There was considerable momentum behind the North's strategy for engaging the U.S. in past negotiations. That is no longer the case, with consequences we have only started to feel.

Abstract:

US-Russia ballistic missile defense (BMD) cooperation can improve strategic stability between both countries, but this cooperation would pose a potential threat to China’s strategic security, especially if it is a closed and deep cooperation. The United States and Russia should make their bilateral cooperation an open regime, and let China and other countries join, so that improvement of US-Russia strategic stability is not based on the sacrifice of strategic stability with China and other countries. China and the United States may also cooperate on BMD in areas of early warning and mutual launch notification. The security costs of these cooperative measures are very low, and the benefits would improve stability, confidence, and mutual trust. Finally, BMD cooperation between the United States
and its East Asian allies (Japan and Taiwan) is threatening Sino-US strategic stability. The United States could improve Chinese confidence by increasing transparency about and limiting the performance of BMD systems.