More than 2,000 people gathered on the Ellipse hours before the showcase demonstration past the White House, the first wave of what organizers said would be the largest Washington rally since the war began. President Bush himself was out of town, monitoring hurricane recovery efforts from Colorado and Texas.

"We have to get involved," said Erika McCroskey, 27, who came from Des Moines, Iowa, with her younger sister and mother for her first demonstration, travelling in just one of the buses that poured into the capital from far-flung places.

"Bush Lied, Thousands Died," said one sign. "End the Occupation," said another.

While united against the war, political beliefs varied in the Washington crowd. Paul Rutherford, 60, of Vandalia, Mich., said he is a Republican who supported Bush in the last election and still does except for the war.

"President Bush needs to admit he made a mistake in the war and bring the troops home, and let's move on," he said. His wife, Judy, 58, called the removal of Saddam Hussein "a noble mission" but said US troops should have left when claims that Iraq possessed weapons of mass destruction proved unfounded.

"We found that there were none and yet we still stay there and innocent people are dying daily," she said.

A crowd in London, estimated by police at 10,000, marched in support of withdrawing British troops from Iraq. Violent clashes between insurgents and British troops in the southern Iraq city of Basra in recent days highlighted the need to get out, protesters said.

"Enough is enough," said Lindsey German, an official of the Stop the War Coalition, which organized the march. "It is now time, once again, for the British people to step forward into the streets and insist that this time we will not be ignored."

Rallies were planned, too, in Los Angeles, San Francisco, Seattle, Florence, Rome, Paris and Madrid.

In a hitch for some coming to the protest, 13 Amtrak trains running between New York and Washington were delayed for up to three hours Saturday morning for repair of overhead electrical lines. Protest organizers said that held up thousands coming to the rally.