President Barack Obama's ambitious plan to begin phasing out nuclear weapons has run up against powerful resistance from officials in the Pentagon and other U.S. agencies, posing a threat to one of his most important foreign policy initiatives.

Obama laid out his vision of a nuclear-free world in a speech in Prague in April, vowing the U.S. would take major steps of its own to lead the way. Eight months later, the administration is locked in internal debate over a top-secret policy blueprint for shrinking the United States' nuclear arsenal and reducing the role of such weapons in military strategy and foreign policy.


Officials in the Pentagon and elsewhere have pushed back against administration proposals to cut the number of weapons and narrow their mission, according to U.S. officials and outsiders who have been briefed on the process.

In turn, White House officials, unhappy with early Pentagon-led drafts of the blueprint known as the Nuclear Posture Review, have stepped up their involvement in the deliberations and ordered that the document reflect Obama's preference for sweeping change, according to the U.S. officials and others, describing discussions on condition of anonymity because of their sensitivity and secrecy.


The Pentagon has stressed the importance of continued U.S. deterrence, an objective Obama has said he agrees with. But a senior defense official acknowledged in an interview that some officials are concerned that the administration may be going too far. He described the debate as "spirited. ... I think we have every possible point of view in the world represented."

The debate represents another collision between the Obama administration and key parts of the national security establishment, following earlier scrapes over troop levels in Afghanistan and missile defenses in Eastern Europe. But more than those issues, the future of U.S. nuclear weapons policy is directly tied to a series of initiatives Obama has advanced as a prime goal of his presidency.

"This is the first test of Obama's nuclear commitments," said former U.S. Ambassador Nancy E. Soderberg, who held senior foreign policy positions in the Clinton administration. "They can't afford to fall short at the outset."

Congress called for the nuclear review, the third such study since the end of the Cold War, placing the Pentagon in charge. Similar reviews were conducted near the beginning of both the Bill Clinton and George W. Bush administrations, but Obama's is the first in which substantial changes stand to be made both in the number of U.S. nuclear weapons and how they are used.

The government maintains an estimated 9,400 nuclear weapons, about 1,000 fewer than in 2002. Obama believes that stepping up efforts to reduce the stockpile will give U.S. officials added credibility in their quest to strengthen the nuclear Non-Proliferation Treaty, the cornerstone international arms control pact.

The timing of the administration debate on the nuclear review is crucial, because a key international meeting on the treaty is planned for May in New York. Also looming next year are other elements of Obama's nuclear agenda, including renewal of an arms reduction treaty with Russia and a push for Senate ratification of a global ban on nuclear testing.

The nonproliferation treaty has been weakened in recent years by the spread of nuclear technologies to countries such as North Korea, Pakistan, and Iran. But non-nuclear countries are wary of intrusive new rules, arguing that while the United States preaches nuclear arms control to others, it has failed to live up to its own promises to disarm.

For Obama, the stakes are high. The difficulties posed by challenges in Afghanistan, Pakistan, North Korea and the Middle East underscore the need for progress on arms control.


Obama was awarded the Nobel Peace Prize in part because of expectations that he would make good on his pledge to reduce the nuclear threat.

He would not be the first president to suffer setbacks on nuclear policy at the hands of politics and the U.S. bureaucracy. Former President Clinton and his defense secretary, the late Les Aspin, had ambitious plans to overhaul nuclear policy in a 1994 review. But it quickly became bogged down in internal disagreement, and ended largely by preserving the status quo.

Obama has vowed to move toward abolition of American nuclear weapons, but has acknowledged the process may not be completed in his lifetime. He told world leaders at the United Nations General Assembly meeting in September that his administration would soon set out a new nuclear posture policy statement that "opens the door to deeper cuts and reduces the role of nuclear weapons."

But the process of doing so in Washington has encountered difficulty on several scores, according to those who described the talks.

A core issue under debate, officials said, is whether the United States should shed its long-standing ambiguity about whether it would use nuclear weapons in certain circumstances, in hopes that greater specificity would give foreign governments more confidence to make their own hard decisions on nuclear arms.

Some in the U.S. argue that the administration should go so far as to assure foreign governments that it won't use nuclear weapons in reaction to a biological, chemical or conventional attack, but only in a nuclear exchange. Others argue that the United States should go farther still, and promise that it would never use nuclear weapons first, but only in response to a nuclear attack.


Pentagon officials question the value of such public declarations, contending that foreign governments may not even believe them, U.S. officials and others said.

During the Cold War, Soviet officials declared that they would only use nuclear weapons in response to a nuclear attack. But when Soviet archives were opened, it became clear that "there were scenarios where they would have contemplated first use," said Charles Ferguson, a former State Department official who now heads the Federation of American Scientists.

The skepticism that resulted could carry over to similar U.S. declarations, limiting their worth, some officials have argued.

A "no-first-use" policy may represent a bigger step than the Obama administration would be willing to take now, private analysts said. Instead, they think the administration might hedge its policy by saying, for instance, that the United States would only use nuclear weapons in situations that threatened its existence, they said.

Another issue being debated is how to scale back the U.S. stockpile while continuing to provide nuclear protection to allies, in part to keep them from developing their own nuclear arsenals. The U.S. maintains hundreds of nuclear weapons overseas for such purposes.

For instance, some U.S. submarines in the Pacific carry nuclear-tipped torpedoes, which many Japanese officials like for their possible deterrent effect against a growing Chinese navy, Ferguson said. Because of the assurance it provides to a key ally, some U.S. officials are reluctant to cut back on the capability.


For similar reasons, some U.S. officials want to keep an estimated 200 nuclear weapons at European bases, providing security for Eastern European countries.

Another debate is whether the U.S. needs three major delivery systems for its nuclear weapons - long-range missiles, submarines and bombers. But eliminating one of them would face strong resistance from affected military services and the lawmakers who support them.

The senior defense official said the "nuclear posture" debate centers on the different ways to the twin goals of nonproliferation and deterrence.

"We are not looking at whether to reduce the roles of nuclear weapons, and whether to reduce [their numbers], we're looking at how," he said.

Julian E. Barnes in Washington contributed to this article.