Since the start of America's nuclear weapons program in 1940, the United States spent $5.5 trillion on it, almost 11 percent of all U.S. government spending, the Brookings Institution reports.

That is 29 percent of all military spending through 1996, the last year studied by the private research group. Despite the Soviet Union's collapse in 1991, the United States is still spending an estimated $35 billion a year on nuclear weapons and related programs, according to the study.Skeptical of the program and whether the deadly U.S. arsenal caused the collapse of the Soviet Union, Stephen Schwartz, chairman of the four-year study, said, "As large as they are, the U.S. government has no clear idea of these overall costs, past or present, because it has never attempted to track them over time."

He also criticized the current U.S. and Russian governments for retaining a formidable arsenal of about 10,000 long-range nuclear weapons each after the end of the Cold War and amid worldwide calls for disarmament.

"The significant costs of maintaining these arsenals will thus continue for the foreseeable future," Schwartz said.

Defending the program and the Clinton administration's approach to arms control, State Department spokesman James Rubin said Wednesday the weapons deterred the Soviet Union and the fact that the program was expensive "should not come as a surprise."

He said administration officials had not had a chance to assess the accuracy of Brookings' estimates, but said, "It was worth the expense; communism was worth deterring through a combined policy of containment and modernization of nuclear forces."

Rubin cited the START II treaty to reduce American and Russian stockpiles of nuclear warheads, which the Russian parliament has failed to ratify, a U.S. drive to trim storehouses of material used to make nuclear weapons, and plans to negotiate another sharp cutback in warheads after the Duma, the lower house in the Russian parliament, takes action on the Start II treaty. The U.S. Senate ratified the treaty in 1996.