Sheehan and several dozen other protesters sat down on the sidewalk after marching along the pedestrian walkway on Pennsylvania Avenue. Police warned them three times that they were breaking the law by failing to move along, then began making arrests.

Sheehan, 48, was the first taken into custody. She stood up and was led to a police vehicle while protesters chanted, "The whole world is watching."

Sheehan's 24-year-old son, Casey, was killed in an ambush in Sadr City, Iraq, last year. She attracted worldwide attention last month with her 26-day vigil outside President Bush's Texas ranch.

Sheehan was among several hundred demonstrators who marched around the White House on Monday and then stopped in front and began singing and chanting "Stop the war now!"

The demonstration is part of a broader anti-war effort on Capitol Hill organized by United for Peace and Justice, an umbrella group. Representatives from anti-war groups were meeting Monday with members of Congress to urge them to work to end the war and bring home the troops.

The protest following a massive demonstration Saturday on the National Mall that drew a crowd of 100,000 or more, the largest such gathering in the capital since the war began in March 2003.

On Sunday, a rally supporting the war drew roughly 500 participants. Speakers included veterans of World War II and the war in Iraq, as well as family members of soldiers killed in Iraq.

"I would like to say to Cindy Sheehan and her supporters don't be a group of unthinking lemmings. It's not pretty," said Mitzy Kenny of Ridgeley, W.Va., whose husband died in Iraq last year. The anti-war demonstrations "can affect the war in a really negative way. It gives the enemy hope."