A dead Prussian haunts the Pentagon, the White House and Capitol Hill. Lately he's been in those Senate hearings on the Persian Gulf crisis, swaggering among the experts, whispering in their ears, seizing their tongues, making them parrot the ideas of a book from another century -- his book.

The experts testify, sagely, that war is nothing but the extension of politics, and that a warring nation must always keep sight of the political objective. His idea. They warn that victory in war does not always go to the side with the most firepower, that war is a contest of will as much as might. His point exactly. The experts sound wise. The Prussian gets no credit.

Only once has his name slipped out. Colin Powell, America's top soldier, was making his introductory remarks on Monday:

"... The fact that military planning must flow from clear political direction is not a new theory. Although we may have had to rediscover it in recent years, I think history will show that it drove Eisenhower and Marshall and Pershing and Grant and Washington, and you can discover that theory in the works of Clausewitz... ."

The ghost surely smiled.

With the United States on the verge of war, one of the most influential strategists of the day is a man who died in the age of muskets. His name was Carl von Clausewitz, and in the early 1800s he wrote a fat book called "On War." He had no inkling of such things as tanks, jet aircraft, submarines, germ warfare or the terrible power of the atom; in his day the tools of the trade were so simple that gun bores were not yet rifled and bullets didn't fly straight. Soldiers fought up close, massed shoulder to shoulder as though in a vast rugby scrum. The commanding general would stand on a hill and survey the entire theater of operations. Maybe sometimes he'd lead a charge himself. That was war, Napoleon-style.

Still, his influence has never been stronger than it is today. Among military analysts, teachers at the war colleges and professional pundits, there has arisen over the past few years a virtual Clausewitz cult.

Twenty-five years ago Senate hearings on the Persian Gulf crisis might have focused on how many soldiers America had, where they would be deployed and whether the tanks would get bogged down in the desert sand. Strategic thinking a few decades ago was largely "Jominian," after Baron Henri Jomini, a Swiss military theorist who was a contemporary of Clausewitz. Jomini focused on the mathematics and geometry of war. "Interior lines" were a major Jominian fetish.

For American leaders today, interior lines are not as important as long-term objectives. It is the term of the hour: Objectives. It's a Clausewitz word. Colin Powell used it 10 times in the first few minutes of his testimony.

Edward Luttwak, a strategist at the Center for Strategic and International Studies, says the Clausewitzian focus on objectives is a sign of enlightenment: "It's a much more mature consideration of war. Instead of saying what are my resources and how do I best manage them, you say to yourself, what is the nature of the enemy, how do I best cope with him, what happens if I win?"

He says that in his testimony before the Senate last week he didn't quote Clausewitz directly because "these aren't supposed to be intellectual discussions." He says mainstream strategic thinking has completely absorbed the principles of the old Prussian. "They don't talk about Clausewitz, not because his influence has waned, but because his influence has triumphed."

Not everyone wants to join the Clausewitz cult. Tom Clancy, best-selling author of make-believe wars, says, "It's just fashion. Clausewitz is just the trendy thing at the time. Why do people have a fixation with the German military when they haven't won a war since 1871?"

Here's why: Vietnam.

"What we found to our amazement is that Clausewitz spoke almost directly to the American experience, like no one else did," says retired Col. Harry Summers Jr., twice wounded in Vietnam and a former professor at the Army War College. He boldly predicts, "Clausewitzian theory is going to define and determine the conflict in Iraq. Whether we realize it or not."

The Clausewitzian Creed With armed hostility seemingly imminent,

with the stakes so high, can't the military find inspiration from someone a little less ... stale? What makes this man so special?

The biography of Carl von Clausewitz can be quickly dispatched. His fighting career started early: He was a corporal at 12. The Prussians were fighting to defend Austria against the French. The Prussians beat the tar out of them but somehow came away with no great political gain. That got Clausewitz thinking. What's the point of war if not to achieve an objective?

He spent the next 20 years in and out of school and war: captured by the French in 1806, teaching at the War College in Berlin in 1808, sojourning with the Russians in 1812 as they fought against Napoleon. Only after Waterloo, when Clausewitz returned to the War College, did he sit down and try to write a book for the ages, a book that would once and for all explain why war exists. War as concept. A big book with a big theme.

"On War" was never actually finished. Clausewitz died of cholera in 1831, having revised only a few sections. His widow hastily assembled a version for publication in 1832. After 20 years the first printing of 1,500 copies had not been exhausted. Not until the Germans defeated the French in 1871 did people pay attention to "On War." In the United States the book finally got its big break in 1976, when scholars Michael Howard and Peter Paret published the first truly readable English translation.

It is not an easy book to dip into, filled as it is with repetitions, contradictions and impenetrable intellectual thickets. But there are a couple of central thoughts, not exactly eloquent but with a powerful simplicity:

"War is nothing but the continuation of policy with other means."

"War is an act of force to compel our enemy to do our will."

Neither of which has quite the punch of Gen. William Tecumseh Sherman's line, "War is hell," or that poster in the 1960s that said, "War is unhealthy for children and other living things," or the opening lyrics to the 1971 Motown hit by Edwin Starr:

"War! Good God, y'all. What is it good for? Absolutely nothing!"

That is not Clausewitzian thinking. Clausewitz clearly says that war is good for something: achieving political goals. "War is not merely an act of policy but a true political instrument, a continuation of political intercourse, carried on with other means. What remains peculiar to war is simply the peculiar nature of its means."

Killing, in short, is a peculiar but sometimes effective form of diplomacy.

Many of Clausewitz's ideas have an obviousness about them that makes one wonder what the fuss is about. For example, his dictum that the military be subservient to the civilian government hardly seems radical.

Yet the failure to heed this simple rule may have brought on World War I. It was a war that unfolded as though war was its own reward. The German military leaders, dominant over policy makers, had their own fancy war plan that called for an invasion of Belgium, but that triggered war with England, which had guaranteed Belgium's sovereignty. The Germans also thought it militarily wise to sink American freighters in 1917, but this drew America into the war and ensured Germany's ultimate defeat.

Clausewitz also said that in order to overthrow the enemy's government it is necessary not only to seize his land but also to pursue and destroy his army. Common sense! Yet when George McClellan commanded the Army of the Potomac during the Civil War, he contented himself with small territorial gains and let the rebel army escape serious harm time and again. Lincoln, fortunately, understood the larger strategic objectives. "Both Lincoln and Grant were Clausewitzians, but neither one of them had ever read Clausewitz," says Civil War historian James McPherson, author of "Battle Cry of Freedom." He adds, "Clausewitz is kind of a bible now for people in military history."

A truly Clausewitzian moment in Vietnam came during the Tet offensive in early 1968. The Viet Cong launched a surprise assault on major South Vietnamese cities, including Saigon. By any traditional measure the Viet Cong were routed. Yet this tactical defeat proved a great strategic victory for the communists, because the American people suddenly realized the true nature of the war, that victory was not in sight. Clausewitz wrote that in war you must strike at the enemy's center of gravity, and for the United States the center of gravity was public support for the war effort. The Tet offensive knocked America on its duff.

"The problem with the Vietnam War was that the value was never established -- that is, the value of the objective -- so that the cost very soon became exorbitant," Harry Summers said recently, speaking in Clausewitzian terms. In a suburb of Washington, Summers, now a syndicated columnist and editor of Vietnam magazine, carries the torch for Clausewitzians everywhere. His 1980 book "On Strategy" became required reading for membership in the Clausewitz cult. The title echoes "On War." Summers's own copy of that classic text shows signs of heavy referencing; the binding is wobbly, the edges of the dust jacket shredded, the pages jammed with paper clips. Seemingly every other sentence is underlined.

"Not that I've got it marked or anything," he said.

Summers experienced a famous moment of Clausewitzian irony. In 1975, on a negotiating mission to Hanoi, he said to a North Vietnamese colonel, "You know you never defeated us on the battlefield."

"That may be so," the other colonel said. "But it is also irrelevant."

Clausewitz as U.S. Policy Unfortunately, Clausewitzian logic doesn't actually solve the problem of whether the United States-led forces should attack Iraq. Once we all agree that it's dreadfully important to heed the objective, to keep the military subordinate to the political leadership, and to be careful out there, what then? Suddenly Clausewitz is as silent as the grave.

In most respects, President Bush has hewed to Clausewitzian principles. He has shown willpower; Clausewitz said war is a contest of wills. Bush has also tried to strengthen the forces in the gulf to a level where battlefield success is likely; Clausewitz said, in his common-sense way, that you shouldn't fight a war if you're not sure you'll win.

Clausewitz might not be as impressed with Bush's ability to clarify American objectives, beyond the removal of Iraq from Kuwait. What then?

Clausewitz said that a war should have popular support. War, he said, is the endeavor of a "remarkable trinity," the government, the military and the citizenry. In Vietnam, public support collapsed beneath the military, and the war was lost. That's why the pundits have criticized President Bush for not doing a better job selling his Persian Gulf policy to the American people.

Public support for war is not just a good idea. It is official U.S. doctrine. The Weinberger Doctrine. On Nov. 28, 1984, then-Secretary of Defense Caspar Weinberger announced that the United States would not go to war unless a number of conditions were met, and as he listed them, it was as though he were quoting Clausewitz. He said we must continually reassess the relationship between our objectives and the military forces in place, and make adjustments if necessary. He said we must have a clear intention of winning -- no muddling around. He said there must be support from the American people and Congress. And war must be a last resort.

Having echoed Clausewitz, Weinberger then quoted him directly:

"As Clausewitz wrote, 'No one starts a war -- or rather, no one in his senses ought to do so -- without first being clear in his mind what he intends to achieve by that war, and how he intends to conduct it.' "

The Clausewitz cult had triumphed: "On War" had become American foreign policy.

The Theory vs. the Reality We don't think of colonels going to graduate school. They do. Colin Powell has studied Clausewitz at the Command and General Staff College at Fort Leavenworth, Kan. There are also a number of places called "war colleges" -- the name a virtual oxymoron. Nowhere is Clausewitz more worshiped than at the Army War College in Carlisle, Pa., which in the spring of 1985 had a Clausewitz Conference and devoted a double-issue of the college's academic journal solely to Clausewitz.

There is even a Clausewitz head.

"Yeah, that's Clausewitz, the hero of the War College," said an officer, pointing out the Clausewitz bust sitting on a pedestal outside the main auditorium. For several years the bust had its own alcove, framed so somberly by red velvet curtains that officers called it the Clausewitz shrine.

"There are people out there in academia who are what I call Clausewitz nuts," said Arthur Lykke, a retired colonel who is one of the senior professors of military strategy. "There was a strong tendency to deify Clausewitz around the 1981-1982 academic year... . This band of Clausewitz nuts was saying, 'If we only had read Clausewitz, we wouldn't have lost in Vietnam.' I think we've passed that."

To which David Jablonsky, another professor, added, joking, "Now they say, 'If we hadn't been in Vietnam, we wouldn't have to read Clausewitz.' "

Most of these instructors have fought in Vietnam. They know war both as a theoretical concept and as a bloody reality. There is something surreal about teaching general principles of war when the mind recalls vivid scenes of carnage. Clausewitz understood that war was horrible, and he didn't try to hide that truth. But there is a great, unbridgeable gap between the idea of war as an extension of policy and the idea of war as the obliteration of human beings.

Col. Phil Thompson, a War College teacher, says, "The older we get, the more faces you see of young kids who died in Vietnam. You see faces but you can't remember names anymore. You see parts of bodies but you can't put the bodies together."

A concept Clausewitz never addressed.