Surveys conducted since the Sept. 11, 2001, terrorist attacks have consistently shown that a majority of Americans favor military strikes against Iraq. But this general agreement that force should be used is neither absolute, unconditional nor uniformly shared by key voting groups, an analysis of recent Washington Post-ABC News surveys suggests.

This ambivalence, most recently reflected in a Post-ABC News poll completed Sunday, raises questions about the depth and durability of public support for using force to topple Iraqi President Saddam Hussein. The poll found that 59 percent of respondents favor using military force against Iraq, even without the support of the U.N. Security Council. But four in 10 supporters also said they had reservations about the looming conflict with Iraq. When these doubters are combined with opponents of military action, the result suggests that more than six in 10 Americans harbor at least some doubts about using force while only a third are unequivocally behind going to war.

The poll also found that some of the strongest doubts about a war with Iraq are coming from a seemingly unexpected source: older Americans, who were far less likely to support taking military action than young adults -- a dramatic illustration of how President Bush's policies have reopened divisions in the electorate that were largely absent immediately before the U.S. invasion of Afghanistan 17 months ago. At the same time, large majorities of Democrats and minorities expressed opposition to taking military action against Iraq.

Taken together, the survey findings illuminate the divisive impact of Bush's aggressive policy on Iraq and the ambivalence of many Americans toward the impending war. They also highlight the narrow margin in which the president has to operate when he orders U.S. troops into battle, and suggest that majority support for war could change quickly to opposition if the conflict goes badly for the United States.

"I have my doubts about going to war," said Rita Scroggins, 29, a homemaker in Groesbeck, Tex., who strongly approves of the job Bush is doing as president but gives him only lukewarm support for his Iraq policy. "We need to have the support of the United Nations to force Saddam out. Then if it comes to war, it would show that the world supports us and it's not just the United States against Iraq."

She is not alone. The need for the United States to win more international support led the list of concerns expressed by survey respondents, followed by fears that a war with Iraq will prove to be too costly in terms of lives lost and money spent.

A total of 1,022 randomly selected adults were interviewed by telephone between Feb. 26 and March 2 for this survey. The margin of sampling error for the overall results is plus or minus 3 percentage points.

The survey found that 34 percent of Americans said they unequivocally favor going to war to remove Hussein, even without the support of the United Nations. Another 24 percent supported using military force against Iraq, but with reservations. Nearly four in 10 -- 37 percent -- said they were opposed to the military option.

"I'd have to see something that proves there really are armaments there that would be dangerous to the United States; I don't see any indication of that now," said Margaret Ward, 68, a retired teacher and Democrat who lives in Shawnee, Okla.

Scott Lehman, 28, a textile worker and Republican who lives in Siler City, N.C., disagrees. "We need to go and take [Hussein] out. They should have done it long before. Everybody I talk to around Siler City approves of it. . . . We don't need nobody else." The views of Ward and Lehman echo some of the traditional opinion gaps on policy questions that have reopened over a possible invasion of Iraq. For example, nearly nine in 10 Republicans -- 86 percent -- support taking military action, compared with 37 percent of all Democrats. Two-thirds of all men favor military action compared with half of all women. Southerners also have been more likely to support the use of military force than the country as a whole.

In contrast, surveys conducted in the months after the Sept. 11, 2001, attacks found significantly less variation in opinion among these groups, largely because each was so lopsided in favor of efforts to punish the perpetrators.

A striking generational gap also has emerged over the issue of war. But contrary to conventional wisdom, it is older Americans who are the most opposed to an Iraq war, recent Post-ABC News surveys have found. In the latest survey, 60 percent of all 18- to 34-year-olds favor military action, compared with 49 percent of those 65 or older.

This generational gap over war did not exist during the post-Sept. 11 invasion of Afghanistan. In Post-ABC News polls conducted during the fall of 2001, older Americans were every bit as eager as the rest of the country to see the U.S. military defeat Afghanistan's ruling Taliban militia.

But public opinion watchers suggest that Afghanistan may have been the exception, not the rule. Older Americans were also more reluctant to invade Iraq in the months preceding the Persian Gulf War of 1991, according to an analysis of Post polls. And experts report the same was true during the conflicts in Vietnam and Korea.

"The problem has been the assumption that because the people on the streets during the Vietnam protests were young, that they represented people that looked like them," said Ohio State professor John E. Mueller, an expert on war and public opinion. But "it's a bad idea to assume they represent their generation."

This pattern is reflected even within political parties; in recent polls, older Democrats were less inclined to support an invasion than younger Democrats. It occurs among men and among women, though it is more pronounced among the latter.

"My hunch is that it's just life-cycle effects," said Lawrence Jacobs, a political scientist at the University of Minnesota. "Folks who lived through wars . . . are just more worldly and seasoned about the many things that can go wrong." For young people, he said, "the tough talk and seemingly surgical nature of what militaries are capable of is very seductive."

These gaps could all evaporate, at least temporarily, when troops actually go into battle. "As soon as the president decides to go to war you'll have unity again," said Stanford University political scientist David W. Brady.

Staff writer Dana Milbank contributed to this report.