The onset of armed conflict in the Persian Gulf has vastly complicated the task of the war's opponents, who began their campaign in a much stronger position than the activists a generation ago who opposed U.S. intervention in Vietnam.

With their country's soldiers now in battle, many Americans who had said they were against military action to drive Iraqi forces from Kuwait now seem to have rallied to President Bush, according to the early polls. In addition, the actual fighting unleashed a wave of anger and bitterness that had largely been absent from the fledgling anti-war movement, leading to a series of disruptive demonstrations that could limit the movement's popular appeal.

Anti-war organizers argue that it would be a mistake to underestimate their movement at a time when all the war news favors the United States. And they have pledged themselves to curbing violent protests, which were often seized upon by the media and helped create an unpatriotic image for the '60s movement.

"What gets attention is divisiveness and violence," said Bonnie Garvin, media coordinator for the National Campaign for Peace in the Middle East, which is organizing a Washington protest march scheduled for next Saturday. "Organize a peaceful march, and you get a yawn."

The first test of her proposition -- and of the movement's base support -- will come today with a march here organized by a competing anti-war group, the National Coalition to Stop U.S. Intervention in the Middle East.

Even before the war began, opponents of military action had expected the president to enjoy an initial surge of support if hostilities broke out and the early success of aerial bombing has raised hopes the war could end quickly. "You have to have a war to have an anti-war movement," quipped Stan Greenberg, a Democratic poll-taker who has worked with peace groups.

But anti-war leaders said the fact that the early news has been so positive would only compound popular dismay -- and expand support for their cause -- if the conflict turns into a much more difficult ground war. President Bush clearly had this in mind when he urged Americans yesterday not to be too euphoric about the early war news.

"Twenty hours into the war, this thing looked terrific -- maybe it's 'Top Gun' after all," said Todd Gitlin, a sociologist at the University of California at Berkeley who has been closely involved with the anti-war movement. "But as soon as it's clear that Saddam Hussein and his armies haven't been deleted from the screen, the anti-war movement will be able to say: 'We told you this would be terrible.' "

Gitlin added that the Iraqi attack on Israel "brings home that a quick and clean surgical erasure is not possible."

With a base more in the churches than on the campuses and with greater initial support among blue-collar Americans, the movement's organizers say they are in a much stronger position than their '60s counterparts to win mainstream support. Greenberg said the large number of Americans who expressed skepticism about the war before it started will move back to the anti-war side if the war drags on.

Heather Booth, a '60s veteran who is now executive director of the Coalition for Democratic Values, a liberal group, added that the new movement is not "playing into a generation gap" over cultural issues and the symbols of patriotism, a fact which limited the appeal of the Vietnam protests.

Indeed, the most striking difference between the old and the new anti-war movements may be the new movement's decision to embrace the men and women of the military and their families.

Still, the earliest manifestations of anti-war rage are likely to play badly with many potential allies. When 17-year old Ryan Calwell burned a flag in San Francisco Thursday, he insisted, according to the Associated Press: "Right now, the flag symbolizes the government, not the people." But such a distinction might be lost on his larger audience.

"The anti-war movement must not be defeated by its most extreme elements in terms of rhetoric, slogans and even violence," said James E. Wallis, a leader of the Washington-based Sojourners, a Christian fellowship.

The outbreak of hostilities has also robbed the anti-war forces of their most broadly popular argument -- that sanctions, not war, represented the best way to defeat Saddam Hussein. And it has opened a new debate over the best approach to ending a war that could exacerbate ideological divisions that have plagued the movement almost from the beginning.

Sectarian infighting among left-of-center groups has already resulted in the two separate anti-war demonstrations here. Further divisions are likely between backers of Israel and supporters of the Palestinian. And there will be new disagreements over whether the movement should emphasize calls for a bombing halt and a negotiated settlement, or insist on complete American withdrawal.

Such arguments, said Robert K. Musil, executive director of the Professionals Coalition for Nuclear Arms Control, could make the movement increasingly irrelevant to the discussions about "policies and outcomes" in Congress.

"The anti-war tactical situation is very difficult right now," Gitlin agreed. "It does become trickier for anti-war people to say something that's practical and compelling and at the same time moral."