For almost half a century, being prepared for World War III has been the military's mission and a piston driving the American economy. Moscow and Washington, East and West, stood toe-to-toe along the Iron Curtain. It took a million soldiers, 12,000 strategic nuclear warheads and a growing defense budget to keep the peace in Europe. Inside a year, the world changed. ``For eons we've been saying, `The Russians are coming, the Russians are coming,''' says Rep. Ronald Dellums, D-Calif. ``Well they haven't come, and they aren't coming.'' Defense Secretary Richard Cheney told Congress: ``We are now on the verge of winning one of the greatest victories in the history of the world without a shot ever being fired.'' Three arms treaties are being negotiated for the signatures of Presidents Bush and Mikhail S. Gorbachev. Once they are settled _ reducing the stockpiles of chemical weapons, conventional forces in Europe and long-range nuclear missiles _ the American military will be transformed in size and purpose. Yet with the outbreak of peace, as Gov. Richard Celeste of Ohio notes, ``there can be a dark side.'' Peace is not a completely comforting prospect for everyone: _Not for the 1,600 people who work in St. Louis at the Army Troop Support Command, distributor of uniforms, tents and other military supplies. The Pentagon wants to close it. _Not for the 101,000 who work for General Dynamics Corp., maker of tanks, submarines, jets and missiles in plants from Florida to California. The No. 2 defense contractor has become a symbol of the end-of-the-Cold War malady. Public relations executive Chris Schildz discourages reporters seeking interviews on how the company is going to handle it. _Not for thousands upon thousands of GIs who now must confront something that American soldiers don't usually worry about _ job security. Today's troops aren't draftees like those let go after World War II or the Korean War or Vietnam. They are volunteers. Many chose the service as a career. Demobilization, for them, is as rude a slap as a layoff for a factory worker. ``We are very well aware of the fact that this is the first time the United States of America has ever taken apart an army made up of all volunteers,'' says Lt. Gen. Gordon R. Sullivan, the Army's deputy chief of staff for operations and plans. He says it's too early to estimate how many soldiers will be let go. _Not for the 13,000 people in and around Lima, Ohio, who owe their jobs to the Army Tank Plant. It makes the M-1 Abrams tank, a 60-ton monster deemed too muscular for the lighter, more mobile Army the Pentagon envisions for the 1990s. The plant is scheduled to close in 1993. Don Downhour, a Lima resident who doesn't work at the plant, says he's sympathetic to the plight of the tank builders, but he sees another side. ``We don't need tanks if we're going to have peace,'' he muses. ``And that's what we've been praying for.'' Harry O'Brien, shop steward at the Saco Defense plant in Saco, Maine, whose mainstay is the Mk-19 grenade launcher, says his co-workers are worried by the defense cutbacks. ``Everybody is saying, `Gee, what happens if we get closed down?','' he says The diminishing of the 45-year-old threat of global war between the two superpowers is worrisome in other places, too: _In President Bush's White House. No sooner had Bush submitted his budget to Congress, calling for a slight drop in Pentagon spending next year, than he took to the road to sell Americans on a single idea: Cutting back too fast, too far is dangerous folly. _At the Pentagon, where Cheney has been carrying the Bush message to Capitol Hill. He is a man in the middle _ knowing reductions will be forced by Congress, but needing to protect Bush's cautious approach and the strategic concerns of the armed forces. _In Congress, where claimants for the ``peace dividend'' _ those who want to retire some national debt; or cut Social Security taxes; or address the problems of the homeless and ill-housed, hungry and poor; or repair decaying bridges, roads and sewage systems; or fix America's education system; or ease the medical-cost burden of the elderly _ are lining up for a piece of the pie. A pie that Bush says doesn't exist. _And again in Congress, where some foresee severe economic upheavals if defense plants and bases close suddenly and thousands of workers are left in the cold. The trouble, then, is figuring out just how much defense to drop, and where. If the Cold War is over, what is the justification for spending 25 cents of every federal dollar on defense _ half of which goes to deterring a Soviet invasion of Europe now deemed less likely than a blue moon? From the fall of the Berlin Wall in November to the Soviet Communist Party's historic decision Feb. 7 to give up its power monopoly, events in the East bloc have eroded the very underpinnings of Western strategic thinking. Indeed, the East European states no longer are a ``bloc'' in the traditional sense. In this new world order, what will the United States do with its military might? Fight terrorists? Play ``policeman'' in Third World hot spots? Revert to the isolationism so dreaded by U.S. allies in Europe and Asia? One answer may be in joining the Bush administration's war on drugs, and the president is pressing for more money to use Marines and other military resources to help keep drugs out of the country. For years the Pentagon fought the idea, arguing it would sap readiness to fight conventional wars and involve soldiers in police work, customarily a civilian concern. Those misgivings seem to have diminished. The exact features of the military transformation are not yet clear, but some signs are visible. U.S. troop strength is being cut, bases closed, weapon programs illed and security threats reassessed. Less clear is what these changes will mean for individual soldiers and their families, for communities and companies that depend on a thriving military-industrial complex, and for a NATO alliance facing possible disintegration. Bush says he hopes attrition will reduce the ranks of the military so that relatively few soldiers will have to be discharged. ``I would like to think that a kid that went in to make a career out of this would not be unceremoniously dumped from the armed services,'' he told reporters recently. As Pentagon planners redefine the military's mission, politicians are rushing to reset the nation's spending priorities. They see a new hope for social programs that took second place to the 1980s military buildup. Sen. Edward Kennedy, D-Mass., has proposed carving out a $169 billion ``peace dividend'' over the next five years _ more than quadruple the savings proposed by Bush in the same period. Rep. Richard Gephardt, D-Mo., accuses Bush of ``beating plowshares into swords.''