In 1945, America had willpower.

At a cost of 400,000 lives, with grim determination, it had waged global war for four years, stopping only when Germany and Japan were vanquished.In 1990, does America have willpower?

Have 45 years of instant victories - such as the Dominican Republic, Grenada and Panama - and long, divisive wars that ended in stalemate or defeat - Korea and Vietnam - sapped the resolve of the United States to sustain a fight?

As Saddam Hussein gains stature as an American bogeyman, and as the whole of Saudi Arabia becomes an American military base, the questions no longer are rhetorical.

Some historians and others suggest that American willpower is and always was conditional. Given a real reason to fight, Americans will fight, they say; given a vague purpose and mounting casualties, they will carp.

Militarily, the U.S. strategy has been to play for time. The blockade of Iraq aims to force Saddam to withdraw from Kuwait - eventually. The troops in Saudi Arabia await an Iraqi invasion that may never come. And if hostilities do break out, no one expects a quick resolution; Iraq is not Grenada.

No one knows whether Americans have the will to support a lengthy, costly war in the Middle East over oil supplies.

"I don't think there's any doubt that if there's a clear and present danger, if there's a Pearl Harbor, Americans would fight a 20-year war if they had to," said James Reston, retired columnist for The New York Times.

"The United States tends to remain at peace or to go to war wholeheartedly, in a crusade," said Robert Maddox, a professor of history at the Pennsylvania State University.

"Americans demand total victory. They want that victory, and then they want to go about their business," he said. "They are no good at dragged-out conflicts, without any resolution, no cities taken."

Few American wars have been supported across the board. During the American Revolution, Tories fled to Canada. During the War of 1812, several New England states threatened to secede. Abraham Lincoln had to deal with copperheads, as Southern sympathizers were known in the North.

The Spanish-American War was short, but the civil war that followed in the Philippines dragged on, spurring American protests led by Mark Twain.

Even the American involvement in World War I, which lasted just a year and a half, inspired disapproval - if only in retrospect.

"By the 1930s, there was a widespread belief among the American people that World War I was a mistake. And we won that war," said Tom Smith, director of general social survey at the National Opinion Research Center at the University of Chicago.

The anti-war attitude - fostered by reports of war profiteering, and by the sense that the war accomplished nothing - hindered Franklin Roosevelt as he tried to bring the United States into World War II.

"Pearl Harbor was an enormously unifying experience," said John Morton Blum, professor at Yale and author of "V was for Victory," a history of the homefront. "There was more unity than in any of the other wars."

Still, there are indications war support was not monolithic, at least when the number of casualties escalated. At the end of 1944, more than 20 percent of those polled favored striking a deal with Hitler.

And in its last year, letters and articles were written decrying the cost of the war in the Pacific, where battles with the Japanese on island after island exacted a heavy toll, said Richard Lingeman, author of the homefront history "Don't You Know There's a War On?"

"People were screaming about it. When they dropped the bomb, there was some relief, I think," said Lingeman.

In Korea and Vietnam, too, war support declined as casualties climbed.

John Mueller, a professor of political science at the University of Rochester, found that support dropped 15 percent when the number of casualties increased from 1,000 to 10,000; it dropped another 15 percent when casualties climbed from 10,000 to 100,000.

The figures for the two wars were identical, though one was conducted under the United Nations flag and one was not; though one was thoroughly televised (a factor often blamed for opposition to the Vietnam War) and one was not.

Any democracy is likely to face similar obstacles during wartime, Mueller suggested. But an authoritarian regime, like Iraq's, may be able quash that kind of opposition, at least for a while.

What would inspire Americans to accept casualties over the long haul?

Another Pearl Harbor, of course. Identifiable enemies help: "We've always needed a recognizable foe - a Kaiser Bill who we were going to hang from the old apple tree, a Hitler," said Penn State's Maddox. President Bush has taken pains to compare Iraq with the expansionist Germany of the 1930s.

Mostly, Americans need a clear and compelling reason. "Sustained belligerency with homefront morale is directly related to purpose," said Blum, the World War II historian.

"That's what was lacking in Vietnam," said Frances FitzGerald, author of the Vietnam history "Fire in the Lake." "It had nothing to do with national willpower."

Would a threat to oil inspire such dedication?

Oil is vital. "We're not talking about selling some bolts of calico cloth or cheap trinkets," the kind of economic interests that sparked American shows of force in the 19th century, said Maddox.

Still, Lingeman recalled that in the months before Pearl Harbor, opponents of intervention said they would not go to war for rubber, a vital commodity that was tied up in the conflict.

"The idea of an economic war, I don't think it will take. I think people would make (economic) sacrifices before they would go to war," he said.

Reston agreed that barring further provocation, American support for a war with Iraq would wilt in the burning sun of the Saudi desert.

"Once the shooting starts, the tendency is to rally 'round the flag. But for a long, long time? No, I don't think so," he said.