The United States revealed for the first time Monday that it has a total of 5,113 nuclear warheads, an unprecedented move meant to bolster arms control efforts.

"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 Clinton said as the Pentagon unveiled figures long shrouded in secrecy.

"We think that builds confidence, brings more people to an understanding of what President (Barack) Obama and this administration are trying to do," she said at a conference in New York on the Nuclear Non-Proliferation Treaty.

The symbolic step was timed to add momentum to the non-proliferation conference and comes after the United States and Russia agreed to new reductions in nuclear weapons.

Independent experts had already estimated the size of the US stockpile over the years, and arms control advocates had said keeping the numbers secret no longer made sense with the Cold War long over.

Clinton said there had been "numerous debates" inside the administration over whether to reveal the figures.

"As of September 30, 2009, the US stockpile of nuclear weapons consisted of 5,113 warheads," the Pentagon said in a statement.

The number included active warheads ready for deployment at short notice, as well as "inactive" warheads maintained at a depot in a "non-operational status," it said.

The figure represented an 84-percent reduction from the arsenal at its peak of 31,255 in 1967 during the Cold War, and a 75-percent reduction from late 1989 when the Berlin Wall fell.

The US government last disclosed details of the stockpile in 1993, releasing figures current up to only 1961.

Clinton said releasing the figures was not "in any way in opposition to our nuclear security" and that experts had already estimated the US stockpile.

A US defense official said the administration hoped more transparency from Washington would set a standard that would encourage countries to be more open.

"We hope that others will follow," the official, who spoke on condition of anonymity, told reporters.

"In particular we'd like to see more transparency from China. We have really quite little visibility into their programs and plans," the official said.

The numbers did not include warheads that are scheduled to be dismantled.

From 1994 to 2009, the United States dismantled 8,748 warheads but "several thousand additional nuclear weapons are currently retired and waiting dismantlement," the Pentagon said.

The US government planned to finish dismantling the weapons "in the early part of the next decade," said an official with the Energy Department.

The figures from the Pentagon appeared to confirm previous estimates from outside arms control experts, who had said the United States had about 9,000 nuclear weapons with 5,000 ready to be deployed.