From coast to coast, Americans are snarling traffic to protest the start of war against Iraq.

About 200 people were arrested Thursday at a downtown Chicago antiwar demonstration, police said.

The protesters likely would be charged with disorderly conduct, failure to disperse and obstructing traffic, according to police spokesman Pat Camden.

Camden said about 3,500 people gathered at Federal Plaza at the start of the demonstrations. But when the crowd marched onto Lake Shore Drive their numbers swelled to an estimated 10,000 protesters.

Television footage showed lines of protesters walking in between vehicles against the flow of traffic. The demonstrators made their way to the intersection of Michigan Avenue and Oak Street, where they were confronted by a large group of police, who appeared to be in riot gear.

Officers were simply following and monitoring the procession, police spokesman Carlos Herrera said.

In San Francisco, at least 500 protesters were arrested (pictured, left) after blocking streets across the city. Police and firefighters used power saws to separate protesters linked with metal pipes. Earlier Thursday, authorities said a scuffle broke out after protesters allegedly tried to take a gun from an officer around 2 p.m.

Police said protesters threw rocks and bottles and one officer was injured -- possibly with a broken leg.

Protesters in Philadelphia blocked the entrances to the downtown federal building, forcing police to detour motorists around the area. About 100 people were arrested.

And a Potomac River crossing into Washington D.C. was shut down during the morning rush hour by as many as 150 demonstrators. Just outside Washington, more than 2,000 high school students walked out of classes in Silver Spring, Md. They circled the school playing drums, guitars and even a trombone.

But some demonstrators support military action. While many students at Brown University in Providence, R.I., held signs denouncing war, Alec O'Neill stood at the edge of the crowd in a T-shirt that read, "I am threatened by Iraq."

People elsewhere who support the war against Iraq also want to share the stage with antiwar demonstrators.

In Lincoln, Neb., more than 200 people waved American flags, sang, cheered and prayed outside the state Capitol Thursday. Several veterans and people with relatives fighting in the war were in the crowd.

In Texas, about a dozen people camped out in Austin near the state Capitol gates to protest the war. But, yellow ribbons began appearing across the state as a show of support for U.S. troops.

In New Hampshire, the House and Senate approved resolutions backing U.S. troops in Iraq.

During the session in the upper chamber, some senators closed a window because of a noisy antiwar demonstration outside.