SANTA MONICA, CALIF. -- When George Bush sits down with Mikhail Gorbachev to negotiate the post-Cold War order, he also will be deciding the fortunes and careers of thousands of Americans who have devoted their working lives to rehearsing war with the Soviet Union.

For four decades of Cold War, these physicists, engineers, political scientists, economists and many other "defense intellectuals" under contract to the Pentagon have replayed scenarios for war in Central Europe over and over. They know every rock and rifle in Germany, every tree and tank in Poland, every meandering stream and missile silo in the Ukraine. They came to understand the minute details of countless battles that have never happened.

They applied extraordinary scientific and technical sophistication to issues such as how the attacked side in a nuclear war might preserve enough weapons to launch a second strike. They understood the inner workings of communist bureaucracies throughout Central Europe and predicted, with varying success, which communist officials were on the rise or fall.

Suddenly, the chief premise of their work -- the notion of a world organized around the U.S.-Soviet conflict -- is falling apart. As a result, the defense intellectuals are scrambling to figure out what to do next. Their jobs depend on their ability to imagine a new world order, a labor for which there is much short-run demand, and on their long-term skill in adapting to a situation few of them predicted.

Many defense analysts say there still will be much for them to do, but some express concern that there will be pressure to invent new threats to U.S. security.

"There is a terrible danger that defense intellectuals will have to go whoring," said Jeremy Azrael, a Soviet specialist at the Rand Corp. here, perhaps the nation's premier military think tank. "Folks in the services will go looking for threats out there." He said defense intellectuals searching for new enemies could soon look like "Diogenes with a lantern peering into dark corners."

The prospect of a new world order is causing excitement and anxiety at Rand's sprawling campus of austerely functional 1950s-style buildings facing the Pacific Ocean. Founded after World War II to give advice and intellectual heft to the Air Force, Rand became the symbol, to the military-industrial complex's friends and enemies alike, of a new style of intellectual endeavor involving a close alliance between the academically-minded and the military, between the thinkers and the fighters.

To their critics, defense intellectuals were "The Wizards of Armageddon," as Fred Kaplan, a Boston Globe reporter, called them in his book on Rand. Men and women who in another age might have pored over Great Books or solved scientific problems turned instead to thinking about war, an enterprise that won ample financing from the growing defense establishment.

Rand's $95.5 million annual budget, 78 percent of which comes from the military, supports about 1,100 people, about one-fourth of whom hold PhDs. Rand's analysts view themselves as independent sorts hired by the various branches of the military precisely because they can offer opinions at least moderately dispassionate.

Azrael said he had been pleasantly surprised by the willingness of most Rand analysts to accept the disappearance of the Cold War world that had been very good to them.

"There was a kind of community vested interest in saying that the world really hadn't changed," he said. "What impressed me is the rapidity with which folks recognized the obvious -- that the world had changed an awful lot."

Still, Azrael and others at Rand worry about what their fellow national-security intellectuals might do just to keep the old business alive. "It may be much harder to stay honest in a world of tight budgets," Azrael said, warning against "new shibboleths" like "the Moslems are going to get us."

The end of the Cold War has forced large changes at Rand, no less than within the Pentagon itself. "Every study has been affected one way or another," said Michael Rich, vice president of Rand's National Security Research Division. "We've canceled some, downsized others."

Among the biggest losers are war between the United States and the Soviet Union in Central Europe, the principal preoccupation of many defense analysts for 40 years.

No war in history, including all those that actually occurred, has been better planned, thought-through, analyzed, acted out on computers and replayed than the one between the North Atlantic Treaty Organization and the Warsaw Pact. "We have a battlefield that's been mapped, instrumented and signed," said James Quinlivan, a program director with Rand's Project Air Force. "Those units that have been there have been planning down to the tree they would have been behind."

Now, it is not only much harder to imagine a war breaking out in Central Europe but also hard to figure out how it might be fought. Rich noted that planners thinking about such a war now have to plan for many more contingencies -- for example, the Poles resisting a Soviet invasion.

A much bigger task is figuring out just how big a military the United States might need and what the military would be used for if the Cold War is truly over.

Like stockbrokers who make a commission whether they buy or sell, Rand analysts who helped plan the military buildup during the Reagan years are hard at work thinking about how to cut defense in the 1990s. "Demand is really very high," said Stephen M. Drezner, vice president of Rand's Army division. "Why is that? Because it's very hard for a bureaucracy to amputate itself."

Russell D. Shaver III, a senior Rand defense analyst with a PhD in applied mechanics, is figuring out what a post-Cold War Air Force would look like. Among his immediate questions: "Should the Air Force of the future be a shrunken version of what it is today, or should it be something completely different?" The answer, he said, depends on the answer to broader questions such as: How little is enough? What do you want a defense establishment to do? What sort of war do you plan against?

Rich said that, in an age of reduced defense budgets, Rand also is seeking cheaper ways to test weapon systems. The goal is to perfect computer simulations so fewer test models of weapons must be built.

Underlying talk of reduced defense budgets is the question of how research of the sort done at Rand will be financed.

Many at Rand say that, in the short run at least, the sort of work they do is just what the military is seeking. Jonathan Pollack, head of Rand's political science department, said services of his analysts are "in huge demand right now," partly because they have always spent time studying countries other than the Soviet Union and partly because they specialize in answering large questions, such as, "What does the new Europe look like?"

Rand's analysts, Pollack said, "don't seem to be lacking for issues to investigate or support for their work."

But Azrael expressed skepticism about the long run, saying he doubts that the military services will be as eager to finance research, given the declining sense of threat. Azrael said he, no less than other academically inclined analysts, believes that pure research is valuable. "That's a wonderful conceit," he said. "But nobody's going to pay for it."

Though Rand analysts condemn threat-mongering, they are laboring mightily to determine the potential source of new threats to the United States or to peace generally. With East-West conflict going out of style, "regional conflict" is the vogue.

Pollack said growth areas for Rand include studies on India, Japan and China. Rand also is undertaking a large study of the Andean nations, in connection with the drug trade, and doing considerable work on the Middle East.

"The truth . . . is that we don't understand where the main thrusts of the world are," Drezner said. "You need concepts of war that may be different from the concepts of war you had before."

People at Rand are a trifle sensitive over the failure of virtually all national-security analysts, including themselves, to predict the upheavals in Eastern Europe. "In no way can you say that any piece of work predicted what would happen in 1989," said Rich, echoing the view of others at Rand.

Rich added quickly that a slew of Rand studies foreshadowed the events of 1989 by demonstrating weaknesses within the Soviet system and the tenuous nature of its ties with its Eastern European satellites. Still, the general tenor at Rand is becomingly modest, a quality not normally associated with defense intellectuals.

"This year, analysts are a lot more humble, and they should be," Drezner said. "If someone tells you, 'Look, I know what's going to happen,' you should put your pen in your pocket. He's in the entertainment business, not in analysis."

The surest sign that the world really is changing is that Rand analysts are now speaking of a kind of intellectual peace dividend -- the possibility of beating intellectual swords into plowshares. They expect to do more work on domestic problems.

Pollack noted that Rand has long been a leading indicator of the government's priorities within the marketplace of ideas. In the 1960s, Rand became engaged in "all kinds of domestic issues," from problems of fire departments to urban poverty. It set up an institute in New York, and by late 1978, fully 50 percent of its budget was dedicated to domestic issues.

Then came the 1980s, Pollack said, "when the defense trough was very full," and Rand shifted its priorities, with the federal government, toward the military. Now, he and others at Rand expect a shift back.

The glimmerings of a kinder, gentler Rand Corp. already are visible in its new thinking about what it wants to study in Eastern Europe. No one ever thought of Rand as an environmental organization, but Drezner said Rand is trying to find environmentalists who specialize in Eastern Europe, to help Eastern European nations with massive pollution problems.

"If you had told me a few years back that I needed an Eastern European environmentalist," Drezner said, "I would have asked: 'What are you smoking?' "