Almost unnoticed in the budget cacophony, Sen. Sam Nunn, D-Ga., the chairman of the Senate Armed Services Committee, called for the withdrawal of 250,000 troops from Western Europe over the next five years.

Nunn told the Senate he now believes removing an average 50,000 a year is a realistic expectation, even though it would leave only a corporal's guard and virtually end the U.S. Cold War presence there.Coming from Nunn, this is more of an edict than a proposal. A lot of out-year promises are being made around here by committee chairmen who know perfectly well they can't or won't deliver. But with Nunn, a hard-liner who is well respected at the Pentagon, declaring it is safe to bring the troops home from Europe, it is a good bet that they will be brought home.

What could upset that timetable, ironically, is arms control. A second round of negotiations on conventional forces in Europe (CFE) is to be devoted to setting ceilings on U.S. and Soviet troop strength in Europe. But in this case, a ceiling could turn out to be a floor. Although 40,000 are to be brought home during the next year, Defense Secretary Dick Cheney and the joint chiefs of staff are sticking with the administration's official position that that will be the end of it for a while. No less than 195,000 American troops must remain in Europe even after the Soviets complete their withdrawal from eastern Germany and other Warsaw Pact states, according to Bush administration policy.

A lot has happened since President Bush came up with that number. The reunification of Germany under NATO has been achieved, to mention one small matter. The Soviets have been making agreements with individual states, including Germany, to get all their troops out of Eastern Europe over the next five years. And U.S. and Soviet negotiators have agreed on a CFE treaty that will be signed later this year putting a lid on weapons in Europe, with provisions for inspection and verification.

Political realities, however, are racing ahead of arms control in Europe. Reasons are fast disappearing for either U.S. or Soviet troops to remain in Europe. What remains aren't security concerns but diplomatic ones.

The first of these is NATO. The U.S. presence in Europe is the glue that has held NATO together, and the concern is that withdrawal would lead to the swift disintegration of that alliance into first a political association and then nothing, once everyone realizes NATO has no useful work left to do. The second diplomatic concern is the CFE II talks themselves. Those negotiations will be devoted to troop levels, and as sure as the sun rises, the administration will argue that Nunn and Congress will undercut negotiators by legislating troops out of Europe.

The only military necessity for remaining in Europe after the Russians leave is geography. The administration contends Moscow could renege on its commitment to get out of Eastern Europe. A successor to Soviet President Mikhail Gorbachev could call a halt to the exodus. Soviet troops and weapons withdrawn behind the Ural Mountains could return to Eastern Europe.

That argument has more or less collapsed with the events of this summer, in which the United States demonstrated it could move a main force of widespread Army, Marine, Navy and Air Force units into the Persian Gulf on short notice, swiftly enough to forestall an invasion of Saudi Arabia by Iraqi troops.

Nunn contends that withdrawing troops from Europe won't necessarily save very much money. Unless units are deactivated, they will still have to be paid and billeted in the United States. And it will cost money to have ships and transports standing by to reintroduce forces into Europe.

What is important, however, is that a hard-line chairman says it is safe to leave. Arguments about saving money can come later.