As the United States moves closer to a possible military confrontation with Iraq, thousands of anti-war protesters gathered in the nation's frigid capital Saturday to voice their opposition to using America's armed forces to topple Saddam Hussein.

Protesters hoped a weekend of demonstrations would win over an American public that polls show is unsettled by the prospect of a war, yet supportive of President Bush's leadership.

The demonstrators sought to make their point in the shadow of America's political and military institutions, rallying in the sub-freezing cold outside the Capitol building before marching to the Washington Navy Yard.

U.S. Capitol Police estimated 30,000 marched through the streets Saturday afternoon, part of a much larger crowd that packed the east end of the National Mall and spilled on to the Capitol grounds.

The Washington protests coincided with rallies in capitals around the world, as anti-war sentiments could be heard from New Zealand to Pakistan, San Francisco to Paris.

Bush was spending the Martin Luther King Birthday weekend at the presidential retreat in Camp David, Md.

"I think the president welcomes the fact that we are a democracy and people in the United States, unlike Iraq, are free to protest and to make their case known," Bush's spokesman, Ari Fleischer, said Friday.

Washington police said they had been assured the main rally and march would be peaceful.

Police issued several permits to the demonstrators, the largest for 30,000 people. On Sunday, a small group planned to march to the White House and promised nonviolent civil disobedience — meaning some expected to be arrested.

"We stand here today, a new generation of anti-war activists," Peta Lindsay from International Answer, the main organizers, exhorted the crowd at the national rally. "This is just beginning. We will stop this war."

Signs branded America a "Rogue Nation," and demanded, "Disarm Bush."

"No war on Iraq," the crowd chanted.

The United States seems to be on a relentless march toward conflict, said Larry Holmes, speaking for the organizers. "It seems like it has a momentum and a sense of inevitability, and so we're rushing against the clock," he said.

"So as they send the troops there and surround Iraq, we're sending the troops into the streets of Washington, D.C., so to speak."

Morning temperatures were in the teens, and organizers tightened their schedule so people would not stand long in the cold.

Three dozen people turned out by the Vietnam War Memorial to show support for President Bush's policy on Iraq and offer a contrary voice to the blitz of demonstrations.

"The protesters don't understand the threat" of Iraqi President Saddam Hussein, said Scott Johnson, 55, a Navy veteran from Minneapolis. "It's a war of liberation for people."

Elsewhere, protesters denounced Bush's Iraqi policy in a major rally in San Francisco, where protesters came by the thousands.

"I'm hoping that the bus loads of people coming as far away as Oregon and Nevada give an indication that this isn't just the crazy loons in San Francisco — but we reflect the opinions of the entire United States," said Tim Kingston of the anti-war group Global Exchange.

In Portland, Ore., police said at least 20,000 people marched through downtown. The eclectic crowd included elderly women in wheelchairs, families with small children, couples with dogs and hooded protesters dressed in black.

In Lansing, Mich., several hundred people met at a church before marching 20 blocks to the state Capitol. "It's just great enthusiasm here, and a great spirit of peacemaking," said the Rev. Fred Thelen from Cristo Rey Catholic Church.

In Des Moines, Iowa, about 125 protesters marched two miles in a bitter wind that made temperatures feel below zero. "Standing out in this kind of temperature is nothing compared to innocent people losing their lives in Iraq," said marcher Eric Kimmer, 32, a credit union worker.

About 400 people, many of them elderly, gathered in downtown Venice, Fla., to listen to anti-war speeches. "America cannot unsheathe the sword, and tell the rest of the world to brandish plowshares," said Methodist minister Charles McKenzie.

Demonstrators staged peace rallies worldwide, events that typically drew hundreds or fewer. But 5,000 people marched through downtown Tokyo, carrying toy guns filled with flowers, wearing face masks that parodied President Bush and waving banners. The crowd, made up largely of students and laborers, was orderly.

About 60 protesters in Hong Kong shouted, "War, no," and in Pakistan, the familiar refrain "No blood for oil" rang out.

Several hundred people tried to march on the U.S. consulate in Lahore, but Pakistani authorities held the crowd back. Six were allowed to deliver an appeal to American officials to spare Iraqis from war.

More than 400 New Zealanders demonstrated in Christchurch. In Moscow, a few hundred people agitated outside the U.S. Embassy in a protest organized by a branch of the Communist Party. People turned their backs to the building, and signs called the United States a "Global Cannibal."

In the Syrian capital, Damascus, thousands marched with a message that was not all about peace. Many cried, "Our beloved Saddam, strike Tel Aviv," in celebration of Iraq's missile thrusts against Israel during the 1991 Gulf War and in hope Saddam would strike again. In the Gaza Strip, Palestinians rallied under the same slogan.

"Bush has said that he intends to launch a pre-emptive war, and now he's facing the most formidable obstacle, which is a pre-emptive anti-war movement," Mara Verheyden-Hilliard, from Partnership for Civil Justice, said Friday.

The Associated Press contributed to this report.