War News Sets a Wave of Protest in Motion Across the Nation : Dissent: Activists clash with police and burn a flag in San Francisco. A march on Washington is planned.

Poised for weeks for this moment, anti-war activists launched a wave of militant and peaceful protests nationwide after news broke Wednesday that the United States and allied forces had attacked Iraq.

A San Francisco demonstration involving thousands of protesters exhibited militancy that activists predict will only grow as the war proceeds. A crowd angrily tore through police barricades, hurled epithets and some bottles at officers and ran a flaming American flag up the Federal Building flagpole.

Their numbers swelling, marchers later went through the largely gay Castro District and through the predominantly Latino Mission District before heading off to the city’s financial district shortly after 8 p.m. Newspaper racks were emptied and dumpsters overturned and set ablaze along the way.

Thousands of leaflets were distributed urging protesters to block both the Golden Gate and Bay bridges today.

At the height of the protest, marchers stood 30 people abreast and stretched for more than 15 blocks. Organizers estimated their numbers at up to 20,000. Officials offered no estimates of their own.

“Now that we’re at war, President Bush said we should pull together and support the war, support our troops,” one speaker told cheering protesters at a rally before the spontaneous march began. “Well, the two are not the same. The best way to support our troops is to bring them home now.”

This comment ignited a chant from the crowd: “Bring them home now. Bring them home alive.” It continued for several minutes.

Elsewhere, demonstrations were smaller and less volatile. In Los Angeles, about 1,000 demonstrators framed Wilshire Boulevard in Westwood, prompting a steady stream of motorists to honk horns to protest the war. In Washington, hundreds marched through downtown, one holding a sign that said “Don’t Bag Our Boys.” Protesters also hit the streets in St. Louis, Portland, Ore., Austin, Tex. , Harrisburg, Pa., and many other cities.

Organizers in national anti-war coalitions say they hope the demonstrations will gain momentum in coming days. A march in Washington on Saturday has been in the planning for weeks. Many protesters say money spent on the military effort would be better spent on education, housing, health care and anti-poverty programs.

The San Francisco demonstration came only a day after an impromptu parade of protesters shut down the Bay Bridge for two hours. Within an hour of news of the war’s beginning, 5,000 people had gathered at the intersection of Powell and Market streets in Union Square.

Clogging traffic, the parade of protesters stretched for blocks on its route through the city. At the federal building, protesters broke through metal police barricades and charged up to a line of San Francisco police officers clad in riot gear.

The crowd stopped short of confronting the officers physically but built a large bonfire on the steps of the federal building and set off fireworks while chanting, “No blood for oil!” Some marchers threw bottles at police, but there were no arrests. Then the crowd surged onward through the city.

Anti-war groups on university campuses escalated protest efforts, and college officials girded for the days ahead. Several thousand protesters rallied at UC Santa Cruz and called for a two-day boycott of classes. College officials said classes will be held as normal.

Anti-war groups called for rallies at UCLA and USC. UCLA’s Executive Vice President Murray Schwartz felt compelled to issue a statement Wednesday night stressing that classes will not be canceled.

Cal State Los Angeles spokeswoman Ruth Goldway said the main concern on campus is that fights might break out because “we have some students from Kuwait and some from Iraq. They might get into arguments hard to control.”

At the Westwood demonstration Tuesday night, Katrina Browne, a 20-year-old UCLA student from Newport Beach, expressed a common sentiment: “I was upset. . . . I wasn’t surprised, but I had that last little bit of hope.”

“I’m not surprised at all,” said Nancy Tuttle, who marched carrying a large picture of her 19-year-old son, an Army soldier now officially at war. “I’m disappointed for the nation and the world.”

At the Federal Building in downtown Los Angeles, more than 150 protesters were arrested in a sit-in a few hours before the war began. Blase Bonpane, director of the Office of the Americas peace group, was struck several times with clubs. Dressed in a suit, an angry Bonpane, in his 60s, said: “We’re trying to protest peaceably, and we’re getting the hell beaten out of us.”

Nicole Dillenberg, 28, of Los Angeles was crying as she sat on the floor waiting to be arrested. Holding out a bleeding hand, she pointed at one officer and screamed, “He smashed my hand. That’s what the First Amendment means in this country in 1991.”

The protests closed the Federal Building for at least two and a half hours.

Harris reported from Los Angeles and Stein from San Francisco. Times staff writer Dan Morain in San Francisco also contributed to this report.