WASHINGTON—The United States has 5,113 nuclear warheads in its stockpile and "several thousand" more retired warheads awaiting the junkpile, the Pentagon said Monday in an unprecedented accounting of a secretive arsenal born in the Cold War and now shrinking rapidly.

The Obama administration disclosed the size of its atomic stockpile going back to 1962 as part of a campaign to get other nuclear nations to be more forthcoming, and to improve its bargaining position against the prospect of a nuclear Iran.

"We think it is in our national security interest to be as transparent as we can be about the nuclear program of the United States," Secretary of State Hillary Rodham Clinton told reporters at the United Nations, where she addressed a conference on containing the spread of atomic weapons.

The U.S. has previously regarded such details as top secret.

The figure includes both "strategic," or long-range weapons, and those intended for use at shorter range.

The Pentagon said the stockpile of 5,113 as of September 2009 represents a 75 percent reduction since 1989.

A rough count of deployed and reserve warheads has been known for years, so the Pentagon figures do not tell nuclear experts much they don't already know.

Hans Kristensen, director of Nuclear Information Project, Federation of American Scientists in Washington, said his organization had already put the number at around 5,100 by reviewing budget estimates and other documents.

The import of the announcement is the precedent it sets, Kristensen said.

"The important part is that the U.S. is no longer going to keep other countries in the dark," he said.

Clinton said the disclosure of numbers the general public has never seen "builds confidence" that the Obama administration is serious about stopping the spread of atomic weapons and reducing their numbers.

But the administration is not revealing everything.

The Pentagon figure released Monday includes deployed weapons, which are those more or less ready to launch, and reserve weapons. It does not include thousands of warheads that have been disabled or all but dismantled. Those weapons could, in theory, be reconstituted, or their nuclear material repurposed.

Estimates of the total U.S. arsenal range from slightly more than 8,000 to above 9,000, but the Pentagon will not give a precise number.

Whether to reveal the full total, including those thousands of nearly dead warheads, was debated within the Obama administration. Keeping those weapons out of the figure released Monday represented a partial concession to intelligence agency officials and others who argued national security could be harmed by laying the entire nuclear arsenal bare.

A senior defense official, speaking on condition of anonymity because the overall total is still classified, did not dispute the rough estimates developed by independent analysts.

Exposure of once-classified totals for U.S. deployed and reserve nuclear weapons is intended to nudge nations such as China, which has revealed little about its nuclear stockpile.

"You can't get anywhere toward disarmament unless you're going to be transparent about how many weapons you have," said Sharon Squassoni, a nuclear policy analyst at the Center for Strategic and International Studies.

Russia and the United States have previously disclosed the size of their stockpiles of deployed strategic weapons, and France and Britain have released similar information. All have signed the Nuclear Nonproliferation Treaty, which is the subject of the U.N. review that began Monday.

The U.S. revelations are calculated to improve Washington's bargaining power with Iran's allies and friends for the drive to head off what the West charges is a covert Iranian program to build a bomb.

Iranian President Mahmoud Ahamadinejad spoke ahead of Clinton at the conference, denouncing U.S. efforts to pressure his regime to abandon its nuclear program.

The U.N. conference will try to close loopholes in the internationally recognized rules against the spread of weapons technology.

Independent analysts estimate the total world stockpile of nuclear warheads at more than 22,000.

The Federation of American Scientists estimates that nearly 8,000 of those warheads are operational, with about 2,000 U.S. and Russian warheads ready for use on short notice.

The United States and Russia burnished their credentials for insisting that other countries forgo atomic weapons by agreeing last month to a new strategic arms reduction treaty.

The New START treaty sets a limit of 1,550 deployed strategic nuclear warheads for each side, down from 2,200 under a 2002 deal. The pact re-establishes anti-cheating procedures that provide the most comprehensive and substantial arms control agreement since the original 1991 START treaty.

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Eds: Associated Press writers Anne Flaherty and Robert Burns in Washington and Matthew Lee at the United Nations contributed to this report.

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