Inside of deactivated Minuteman II intercontinental ballistic missile silo in Wall, South Dakota. (Photo: AP)

(CBS/AP) The United States is cutting its back-up supply of nuclear weapons while bolstering its ability to build new and better bombs if necessary, the Energy Department said Thursday.

"By 2012, the United States' nuclear stockpile will be the smallest it has been in several decades," National Nuclear Security Administration administrator Linton Brooks said in a letter to Congress presenting a classified report on the nation's nuclear arsenal.

The changes to the nuclear stockpile follows President Bush's commitment in 2001 to cut the number of nuclear missiles deployed around the world to 1,700 to 2,200, a reduction of two-thirds. The stockpile is the backup supply for operational missiles.

"The president's decision to reduce the number of operationally deployed weapons has laid the groundwork for a major reduction in the size of the total nuclear stockpile," Brooks wrote. His unclassified letter did not specify the size of the stockpile or the proposed reduction.

According to The New York Times, Brooks told a conference call with reporters the move would cut the stockpile "almost in half." A weapons expert at the Natural Resources Defense Council, Tom Cochran, told The Times that the total nuclear arsenal would drop from 10,000 weapons to 6,100 after the reductions announced Thursday.

Even as it has looked to cut the active nuclear arsenal, the Bush administration has also signaled it is interested in developing the capability to build newer, more advanced weapons.

One such weapon is the B-61-11 nuclear bunker buster.

Brook's letter indicated the reduced stockpile would not derail those efforts; in fact, it might speed them.

"We recognize that maintaining the nation's nuclear deterrence with a much smaller stockpile means that we must continue Administration efforts to restore the nuclear weapons infrastructure," he wrote.

According to Brooks, those efforts include planning a new facility for making the plutonium pits in nuclear weapons, improving training for weapons scientists and "enhanced test readiness.

The U.S. conducted its last nuclear test in 1992. While the White House opposes the Comprehensive Test Ban Treaty — which the U.S. has signed but not ratified — the administration says it has no plans to conduct a test.

Last summer, nuclear officials from several agencies met for a meeting that included discussion of the question: "What is the uncertainty in confidence and potential risk threshold for a test recommendation—what would demand a test?"

The administration has also pushed for research on low-yield nuclear weapons and a bunker-busting nuke called the Robust Nuclear Earth Penetrator.

A 2002 Nuclear Posture Review identified Iraq, Iran, Syria, Libya, North Korea as countries where "contingencies" could arise for which U.S. "nuclear strike capabilities" must be prepared, according to a leaked version.

• The Senate on Thursday agreed to ease cleanup requirements for tanks holding millions of gallons of highly radioactive waste from Cold War-era bomb making. The provision allows the Energy Department to reclassify radioactive sludge in 51 tanks at a South Carolina nuclear site so it can be left in place and covered by concrete, instead of being entombed in the Nevada desert. Senate critics said the change would leave poisonous sludge in underground tanks and risk contamination of groundwater.
• Federal environmental regulators have rejected a government plan to begin removing highly radioactive waste from a former uranium-processing plant in Ohio. Nevada has threatened a lawsuit to block the Energy Department from shipping the waste from the former Fernald plant to the department's desert disposal site 65 miles north of Las Vegas. The Environmental Protection Agency told the Energy Department on Tuesday that it should not start removing the powdery waste from a concrete silo later this month and then hold it at Fernald until it could be shipped.
• Pakistan successfully test-fired a medium-range, nuclear-capable missile Friday for the second time in a week, but officials said the test was not intended as a message to neighboring India's new government.
• Prime Minister Abdullah Ahmad Badawi said Friday that there was no need to let international investigators interrogate the alleged chief financial officer of a nuclear trafficking network arrested recently in Malaysia. Malaysian officials already have ruled out allowing U.S. officials to question Buhary Syed Abu Tahir, saying they don't want any "foreign intervention" in the case.