The day after war began, antiwar protesters here and across the country took their anger and dismay to the streets, from rallying and marching to blocking intersections, paralyzing traffic and getting arrested.

Peace vigils and rallies took place in approximately 500 cities nationwide and in hundreds of cities worldwide. There were marches and demonstrations from Palm Springs, Calif., to Palm Beach, Fla., and from Iceland to Indonesia. Thousands of protesters in scores of cities throughout this nation also made good on their promise to engage in mass civil disobedience and disrupt business as usual the morning after President Bush ordered the attack on Iraq to begin.

In Philadelphia, 100 protesters were arrested after blocking the entrances to the downtown federal building. In New York, more than 300 protesters converged on Times Square at the afternoon rush hour, blocking traffic.

Everywhere, dissenters made their presence known. In Cambridge, Mass., Harvard students and faculty members walked out to protest the start of war, as did students in universities and high schools in dozens of cities. About 200 students at the University of California at Berkeley staged a sit-in this afternoon after a noon demonstration of more than 1,500 students and teachers.

Other protests drawing from a couple of dozen to many hundreds were staged in cities such as Boston, Chicago, Minneapolis, Salt Lake City and Seattle.

In Chicago, traffic was shut down on Lake Shore Drive, one of the city's main arteries, for about an hour this evening as more than 10,000 marched north from the Federal Plaza. Large numbers of police in riot gear were brought in as the marchers tried to turn along Michigan Avenue, the city's main upscale shopping district. "This was a nice turnout against the war," said Brian Harris, 30, a cataloguer for a theological library. "I protested during the Gulf War here, but I think this is a lot bigger."

Perhaps like nowhere else, in San Francisco the streets belonged to the antiwar protesters today. (Washington was second to San Francisco in the number of actions planned today to protest the war.) They began congregating at the city's major intersections at 6 a.m. and had shut down most traffic through the financial district within the hour.

Buses, idled on the streets, were abandoned by their drivers. Cars were rerouted so far off the beaten paths that major streets were emptied. And while police in riot gear kept arresting protesters -- using firefighters with saws to cut through plastic and metal tubes that demonstrators used to link themselves to one another -- there always seemed to be another wave of protesters at another intersection.

At rush hour, commuters were backed up on the Bay Bridge for nearly a mile as protesters blocked the off ramp into the financial district until police arrived. At noon, demonstrators were still moving, and portions of major streets were blocked. At least 300 protesters also tried again to block the Bay Bridge, but police steered them away.

More than 1,025 people had been arrested by late this afternoon and protests continued well into the evening as demonstrators continued blocking streets and harassing motorists.

Many of the protests today across the country were part of nonviolent antiwar demonstrations organized by the Iraq Pledge of Resistance, a coalition of 55 peace groups in the United States. Gordon Clark, the coalition's national coordinator, said that acts of civil disobedience are planned for tomorrow and the day after and the day after that.

"We've had 28 cities sign up today," he said this afternoon from Washington. "We can't even keep up with the number of cities planning C.D."

In San Francisco, the civil disobedience was highly organized. . Protesters risked arrest by sitting in the middle of the streets, while hundreds more cheered them on at each blockade. Those on the sidelines operated like support groups. They shouted, "We love you! You're our heroes!" to protesters as they were arrested, and chanted, "The whole world is watching!" every time it looked as though a situation between police officers and protesters might get out of hand.

Donald Livingston, a 47-year-old financial analyst, was on his way to work, marching through what looked like a parade of suits, when he changed his mind and joined the protesters.

"I'm from Ohio," he said, "and when I went back home last week, I found that everyone I talked to, from the gas station cashier to the guy who parked my car, was against this war. This morning, I decided that it's important for those of us who are against it to show it, so that we can prove that the polls are dead wrong. The majority of Americans do not want this war."

While today, as the Day After, was the first time such a mass civil disobedience was planned, organizers said it would not be the last. "People are going to try to stay in the streets," said Jason Mark of Direct Action to Stop the War, a San Francisco-based network of activists offering training and guidance to those who want to commit civil disobedience. "People are committed to coming on the streets tomorrow and the day after that."

Special correspondent Kari Lydersen in Chicago contributed to this report.

A protester, with his son on his shoulders, is arrested Thursday during an antiwar sit-in at Beale and Market Streets in San Francisco.Loretta Linseed of San Francisco, left, yells as firefighters saw through plastic and metal tubes that war protesters used to link themselves together in order to block Market Street in San Francisco's financial district.