Galvanized by the American attack on Iraq, anti-war activists around the country set off their own barrage of street protests, chaining themselves together, blocking workers and traffic, walking out of classes, and parading in mock chemical suits. Hundreds were arrested from San Francisco to Washington, D.C.

But the anti-war groundswell brought out thousands of counterdemonstrators. One in Mississippi carried a sign saying, "Support the U.S. or keep your mouth shut."

Thursday was one of the heaviest days of anti-government protesting in years.

"This is no ordinary day," said Jason Mark, a San Francisco activist. "America is different today: We've just launched an unprovoked, unjust war."

One protester died after tumbling from the Golden Gate Bridge. Authorities were investigating the death as a possible suicide.

San Francisco had some of the largest anti-war activity, hobbling the morning commute. Thousands in roving bands temporarily took control of some downtown streets and closed several exits from the San Francisco-Oakland Bay Bridge. Smaller splinter groups broke windows, heaved debris into streets and occasionally scuffled with police. Some protesters hurled rocks at trains, briefly halting service at a station in nearby Oakland.

Police wearing helmets and carrying nightsticks made at least 350 arrests.

"We don't want to alienate people. I hope people realize that political murder merits action that inconveniences them," said protester Quinn Miller, who took the day off from his banking job.

Close to 200 people joined anti-war rallies throughout the day in Columbia, Mo., marching to Rep. Kenny Hulshof's district office and then to the local mosque.

Anti-war banners were evident all day around the St. Louis area, hanging from buildings and freeway overpasses, some simply bearing a peace symbol.

In Missouri's capital

In Jefferson City, a couple dozen protesters with anti-war signs gathered outside the federal courthouse -- just across the street from the Capitol. Other Missouri protests were held in Springfield and Carthage.

In Washington, dozens of activists temporarily shut down inbound lanes of a Potomac River crossing, holding up the morning commute. Outside the White House, about 50 stood in chilly rain and shouted, "No blood for oil!"

Anti-war activists in Philadelphia blocked entrances to the downtown federal building, forcing police to detour motorists away from the area. Police arrested 107 protesters.

In New York, about 350 rallied at Union Square under a steady drizzle.

About a dozen students lay down in black garbage bags. "We're expressing how the Iraqis are being killed for no reason," said Rachel Klepner, 14, who left class at Beacon High School for the protest.

In Massachusetts, students and professors walked out of college classes around the state in protest of war. At the Massachusetts Institute of Technology, in Cambridge, about 600 students converged on the student center, some chanting and wearing mock biochemical protective suits.

Other demonstrations were more solemn, with the reciting of Christian, Jewish and Muslim prayers through a bullhorn at a federal building in Pittsburgh.

A number of demonstrations reflected backing for the war effort or support for U.S. troops.

Some 2,000 people gathered outside the state Capitol Thursday in Mississippi, a state that has seen 4,500 guardsmen and reservists activated during the buildup to war and where many families also have relatives in the military full time.

In Lincoln, Neb., more than 200 people sang, cheered and prayed outside the state Capitol.

Sheila Murphy, who works with families who have members in the Nebraska Air National Guard, said, "This is a time they need to know that everyone is behind the troops and supporting the troops."

On the edge of a protest at Brown University in Providence, R.I., a young man stood in a T-shirt that read "I am threatened by Iraq" in front and "Regime change now" in back.

An anti-war group, West Virginia Patriots for Peace, placed candles and flowers outside a federal courthouse in Charleston. Members said they wanted both to protest the war and support U.S. troops.

"We don't want our men and women over there to feel like they did in Vietnam," said Barbara Ferraro.

Abroad, hundreds of thousands of protesters marched Thursday on American embassies in Athens, Paris, Manila in the Philippines, and other cities. In Cairo, police sprayed soapy water and used dogs to keep back thousands of protesters, including some who threw rocks and pounded on cars.