By MATTHEW L. WALD WASHINGTON, Aug. 20 — A program conceived by the Clinton administration to rid the world of 100 tons of American and Russian weapons-grade plutonium is likely to be abandoned by the Bush administration, according to people who have been briefed about the project. Under the plan, which was first proposed in the mid-90's, 50 tons of American plutonium and 50 tons of Russian plutonium would be taken out of nuclear weapons and either converted into fuel for nuclear reactors or rendered useless for weapons by mixing it with with highly radioactive nuclear waste, a process known as immobilization. When the plan was drafted, Clinton administration officials said the program would reduce the risk that the plutonium would fall into the wrong hands, where it could easily be turned into weapons. By reducing the availability of weapons-grade plutonium, the project had the added benefit of bolstering treaties between the United States and Russia to cut the number of nuclear warheads deployed by each side, by making it harder to turn plutonium from decommissioned weapons back into warheads. Bush administration officials deny that the program is dead, but acknowledge that it has difficulties, primarily financial ones. "The issue is under review," said an administration official who would speak only if not identified. "We've made no secret of that. But no decisions have been made." But the official continued, "It's no secret that there are a lot of equities to balance here." One major equity, he said, is money. Early this year the Energy Department predicted a cost of $6.6 billion, about triple the initial estimates, to convert the American stocks to fuel for civilian nuclear reactors. It put Russia's cost at $1.76 billion, which is money Russia does not have. The expectation under the Clinton administration was that the United States and other rich countries would help pay, but no concrete pledges were ever made. In 1999 the Clinton administration did agree to pay a consortium of power companies $130 million to use plutonium that the government would convert into fuel. But the conversion factories are not yet built, and the conversion itself was contingent on an agreement with the Russians to take similar steps to dispose of plutonium from their weapons. Despite the program's expected benefits, the Bush administration's proposed Energy Department budget this spring did not include the money needed to mix some of the plutonium with nuclear waste. The second path — converting it to fuel for American nuclear reactors, the strategy the Clinton administration hoped would induce the Russians to do the same — also appears likely to be dropped soon. "There is no enthusiasm for it whatsoever," said a Congressional aide who was briefed by officials of the National Security Council, referring both to the current strategy of immobilization and to conversion to reactor fuel. The issue of what to do with plutonium from decommissioned nuclear weapons has haunted policy makers for years. One particular fear is that the material from Russian weapons would be bought or stolen by terrorists or a "rogue" government who could construct a nuclear bomb. In recent years, the security of bomb materials in Russia has been improved markedly by joint Russian-American efforts, administration experts say. Bush administration officials insist that they share the goal of disposing of American and Russian plutonium. "There's no philosphical shift that says suddenly we're perfectly fine with surplus plutonium laying around — we're not," said an administration official familiar with the Clinton-era program. But, he added, conversion to fuel for existing reactors or mixing with waste are "not the only options for disposing of it safely." As an alternative, the Bush administration appears to be considering a variety of untested technical options, including a new generation of nuclear reactors that could burn plutonium more thoroughly. "They're trying to improve on it by giving up on getting started any time soon," said Matthew G. Bunn, a nuclear expert at the Kennedy School of Government at Harvard, who was an adviser to the White House Office of Science and Technology Policy in the Clinton administration. He and other experts are skeptical that a new generation of reactors, which was also mentioned in President Bush's energy plan as a way to dispose of nuclear waste, would ever be built. Construction on the last nuclear plants built in the United States country was begun more than 25 years ago. "We're back at Square 1 with the program, and they're looking at imaginary options, like advanced reactors," said Tom Clements, executive director the Nuclear Control Institute, a nonprofit group that opposes the use of plutonium for reactor fuel. "For financial reasons, it's not going to be viable." Though the administration is considering dropping the program to convert or immobilize weapons- grade plutonium, a separate Russian-American program to reduce the inventory of another Russian bomb fuel, highly enriched uranium, is continuing. In fact, uranium that was intended for Russian bombs now meets more than half the needs of American power reactors. But diluting uranium to the type used in power plants is technically far simpler and cheaper than the process required for plutonium, which must be converted from the metal form used in weapons to a plutonium-uranium ceramic used in American power plants. In fact, enriched uranium has economic value as reactor fuel, while converting plutonium appears to be a money-losing proposition. Even so, Russian officials have said repeatedly that they view plutonium as an asset and would like to build new breeder reactors, so named because they produce plutonium faster than they consume the other main reactor fuel, uranium. The end of the plutonium program would be mixed news for groups concerned with proliferation. For example, the Nuclear Control Institute has pushed vigorously for immobilization and against converting plutonium to reactor fuel, which is known as mixed oxide, or MOx. Officials of the institute say conversion to MOx is very expensive and would encourage international commerce in weapons material. "We think their assessment of MOx is correct," said Mr. Clements, referring to the administration. "The problem is, it appears they've also rejected the cheaper alternative, which is immobilization." Copyright 2001 The New York Times Company