At the same time, the Energy Department announced plans to consolidate the nuclear weapons complex that maintains warheads and dismantle those no longer needed, saying the current facilities need to be made more efficient and more easily secured and that the larger complex is no longer needed.

"We are reducing our nuclear weapons stockpile to the lowest level consistent with America's national security and our commitments to friends and allies," White House press secretary Dana Perino said. "A credible deterrent remains an essential part of US national security, and nuclear forces remain key to meeting emerging security challenges."

The government will not provide any numbers on the overall size of the nuclear stockpile, but there are believed to be nearly 6,000 warheads that either are deployed or in reserve.

Separately, under terms of a 2002 arms control treaty with Russia, the US is committed to reducing the number of deployed warheads to between 1,700 and 2,200 by 2012.

Three years ago, Bush said he wanted the overall stockpile reduced to half by 2012, but officials said that goal now has been reached so further reductions are being made, resulting in the new targets for 2012.

The Energy Department has been examining ways to consolidate the complex of weapons stockpile-related facilities at eight major locations across the country. They include federal research laboratories and other sites involved in nuclear stockpile stewardship and warhead dismantlement.

"Today's nuclear weapons complex needs to move from the outdated Cold War complex into one that is smaller, safer, more secure and less expensive," said Thomas D'Agostino, administrator of the National Nuclear Security Administration, which oversees nuclear warhead programs within the department.

Under the consolidation proposal, which must still go through formal environmental reviews, special nuclear material used in weapons will be moved to five sites by the end of 2012 and the overall work force will be reduced by 20 to 30 percent.

While none of the eight major facilities will be closed, about 600 buildings or structures will be closed or shifted to non-weapons activities and two testing facilities supporting weapons labs will be closed.

While the consolidation reflects the reduction in the size of the warhead stockpile, it also has been prompted by growing concern over the ability to provide adequate security over the larger complex as security demands have increased sharply since the Sept. 11, 2001, terrorist attacks.

Some of those security demands have been viewed as far too expensive under the current spread of nuclear materials -- plutonium and highly enriched weapons-grade uranium -- within the complex.

The NNSA announced in September plans to consolidate plutonium from sites in Washington state, California and New Mexico to the Savannah River facility in South Carolina for storage and conversion.

Meanwhile, the administration faced a setback in its hopes of developing a new, more reliable and robust warhead that would eventually replace the existing, aging warheads.

The broad omnibus spending bill expected to be approved by Congress eliminated money for the Reliable Replacement Warhead for the current fiscal year. The administration had asked for $88 million for design and preliminary work on the proposed warhead.

"This (warhead) would have sent the wrong signal around the world encouraging the very proliferation we are trying to prevent," Sen. Dianne Feinstein, D-Calif., a critic of the new warhead program said.

NNSA spokesman Bryan Wilkes said the funding cut was disappointing.

"This program is intended to establish the feasibility of a more secure and safer warhead that would help to assure long-term confidence in the reliability of the nuclear weapons stockpile without nuclear testing," Wilkes said.