Tens of thousands of protesters, from as far away as Colorado and Maine, converged on Washington yesterday in a sea of waving flags and banners in what appeared to be the country's largest anti-war demonstration since the start of the Persian Gulf War.

The crowd, estimated at 75,000 by police and at least 250,000 by march organizers, was protesting a war that most Americans support. A nationwide Washington Post-ABC poll last Sunday said 75 percent approved of U.S. policy, while 23 percent disapproved.

So dense was yesterday's crowd that the demonstrators appeared to march in a continuous parade 30-people wide for more than three hours as they wended their way from the Mall up Pennsylvania Avenue NW, around the White House and then to the Ellipse, where the demonstration ended with a rally of speeches and song.

"This makes a visual statement that shows there is a tremendous opposition to the war," said Bonnie Garvin, media coordinator for the National Campaign for Peace in the Middle East, the rally's organizer.

A Washington Post survey of 827 demonstrators yesterday showed that more than half had attended at least one other protest against U.S. policies in the Persian Gulf, and a substantial majority came from outside Maryland, Virginia and the District. {See story on Page A21.}

The demonstration was in contrast to last week's war protest here, which drew crowds estimated by police at 25,000 and by organizers at 100,000. Last week's protest was angrier in tone, and many of those who came said they were affiliated with left-wing groups and a range of radical causes. The organizers of that rally refused to condemn Iraqi President Saddam Hussein, and objected to the economic sanctions against Iraq approved by the United Nations.

The mood of yesterday's crowd was more upbeat, and the message was almost exclusively anti-war. Those participating, although predominantly youthful, also appeared to represent a broader cross section of Americans, and most interviewed were highly critical of Iraq and Saddam.

"I dislike Saddam Hussein intensely," said Bob Corbett, 54, a university professor from St. Louis, who took an 18-hour bus trip to come here, arriving at 6 a.m. yesterday. "But the U.S. being there poses a much greater danger to the Middle East."

Until now, the nation's largest anti-war rally was one in San Francisco on Jan. 19, which police said was attended by 35,000. Eleven demonstrators were arrested here yesterday, most of whom were in a group that sat in the middle of Pennsylvania Avenue in front of the White House about 7 p.m. District and Park Police gathered on three sides of the group and gradually forced it back into Lafayette Square.

Yesterday's march, which started about noon at Third Street NW and the Mall, at times had a festive air. Onlookers lined the march route to applaud Vermont's Bread and Puppet Theater, which staged an elaborate show that included dozens of masked performers dressed as skeletons and mourning mothers carrying dead bodies.

Dozens of American flags were waved throughout the march, and demonstrators repeatedly stressed their patriotism in interviews. Students from Sidwell Friends School in the District marched in line with five American flags with the words "NO WAR" attached to the poles. "We're protesting the war because we love our country," said sophomore Vashti Van Wyke.

Cynthia Smith, a 30-year-old Medicaid employee from New York, looked out at the marchers and said that for the first time in her life, she felt a commonality with people of many races. "Today is the first day I ever felt American, not black American, but American," she said.

Small crowds of demonstrators supporting the war effort, vastly outnumbered, dodged in and out of the march, chanting slogans in support of Bush and "U.S.A., U.S.A." There was some shoving between the groups, but march monitors usually separated them by forming human chains.

Holding a flag, nose to nose with anti-war demonstrators who circled him near the White House, a man in his twenties debated all comers. He defended the American troops and Bush's policies.

"It's the '60s all over again," he said, mocking the crowd, in particular men with long hair and beards. "I'm so happy these guys have a place again."

Nearby, two women, one in combat fatigues and the other holding the Marine Corps flag, were approached by several women carrying anti-war banners. "All we say is that you educate yourselves," said one woman, a "No War" sign dangling from her neck.

"And what makes you think that if we educate ourselves we'll think like you?" replied one in the crowd.

About 300 local protesters rallied in Meridian Hill Park, then marched down 14th Street NW and joined the main parade on Pennsylvania Avenue. Sponsored by the National African-American Network Against U.S. Intervention in the Gulf, the local rally drew a relatively small crowd despite widespread distribution of fliers.

Meanwhile, there were smaller rallies across the nation supporting U.S. policy in the gulf, including one in Goldsboro, N.C., home of Seymour Johnson Air Force Base, with 8,000 demonstrators, and another in Winston-Salem, N.C., with 3,000 people. "We don't want there to be any doubt in {soldiers'} minds about our support," said Winston-Salem Mayor Martha Wood.

About 400 supporters of U.S. policy sang "The Star-Spangled Banner" on the Massachusetts statehouse steps. "The silent majority is no longer silent," said Mike Scott, of Cambridge, a founder of the sponsoring group, Support Our Soldiers, and father of a Marine in the gulf.

Bertram A. Weinert came to the Washington march wearing a pocketful of medals, including the Purple Heart he was awarded in World War II after being struck in both legs with machine gun fire. Weinert, 65, director of consumer education for the New York State Attorney General's Office, said he came because "what was worse than being wounded was knowing that I killed someone."

Weinert said that he did not have "a positive feeling about Iraq" but that he believed a diplomatic solution was possible. He called the bombing of Iraq "disgraceful."

Many Jewish demonstrators said they were in anguish because of Iraq's missile attacks on Israel but still felt compelled to demonstrate. "I think Jews with a broad vision also feel the enormous sense of loss all over the Middle East," said Mark Blumberg, 45, who drove from Boston yesterday morning. Blumberg stood at the side of the march holding a sign: "Another Jewish Voice Against Military Madness and a Spiralling Slaughter."

Although some in the crowd described themselves as veterans of the anti-Vietnam War movement, a significant proportion said the protest was their first. Many said they had come with feelings in conflict.

Pat Duquette, 42, a paralegal and mother of three from Westchester County, N.Y., said she initially was afraid she was "going to hurt the troops" by demonstrating. Her husband and eldest son disagreed with her participation, she said, but she decided she "had to take a stand."

Gary Nowak, a 25-year-old bank employee and Marine reservist from Chicago, said his resolve against the war had been strengthened by Iraq's apparent release of millions of gallons of oil into the Persian Gulf. Standing beneath a large banner bearing the phrase "No blood for oil," he said, "It makes me a lot more upset."

At the Ellipse, several speakers addressed the crowd, including Rep. Charles B. Rangel (D-N.Y.), Jesse L. Jackson and Molly Yard, president of the National Organization for Women.

Brenda Reed, an Oakland woman whose husband was killed in Vietnam, held up the folded American flag she received upon her husband's death. "I learned the hard way there is no glory in a folded flag," she said. As Reed spoke, tears streamed down the face of a man who described himself as a Vietnam veteran who supported having a defensive force in Saudi Arabia. A lawyer in Rockville who declined to be identified said he had come to the march because he had a son in college. "I think there are a lot of people holding their breath," he said.

Staff writers DeNeen L. Brown, Gabriel Escobar, Jeffrey A. Frank, Veronica Jennings, Brooke A. Masters, Eric Charles May, Mary McGrory and Saundra Torry contributed to this report.