Some protesters chanted “No blood for oil.”
Among the other groups protesting were Code Pink, Veterans for Peace, Peace Action, and United for Peace and Justics.
Groups supporting the war were also present. A handful of people gathered at a nearby armed forces recruiting center.
“We’re out here to show support for our troops on the anniversary of the liberation of Iraq,” said Kristinn Taylor, 45, of the District.
Colby Dillard held a sign reading “We support our brave military and their just mission” and pointed to red paint that one of the protesters had splattered on the sidewalk.
“The same blood was spilled to give you the right to do what you’re doing,” Mr. Dillard, who served in Iraq in 2003, told the protesters.
Earlier in the day, about 150 people, mostly with the group Veterans for Peace, marched down Independence Avenue Northwest. Many of them carried upside-down American flags, which they said symbolized a nation in distress.
Police also tussled with protesters over the yellow tape they tried to string along the fence protecting the White House, after they held a waterboarding demonstration. Nobody was injured and no arrests were made.
Daniel Black, who was stationed in Fallujah with the Marines in 2004, said that after he returned, he came to believe the war was a mistake.
War protests on Washington have slowly dwindled since their height on Oct. 21, 1967. An estimated 50,000 people marched in front of the Defense Department’s headquarters and roughly 600 protesters were arrested.
In January 2007, tens of thousands, including actress and Vietnam-era protester Jane Fonda, came to the District for weekend protests. There were reports of only minor incidents and a handful of arrests.
Elaine Matthews of the Granny Peace Brigade said yesterday that of the main presidential candidates, Sen. John McCain, a Republican is the “worst” on Iraq and Sen. Barack Obama, Illinois Democrat, is the best. However, Mrs. Matthews, 57, said Mr. Obama is still too “warlike,” despite his commitment to leave Iraq.
Similar protests were held yesterday throughout the country.
About 20 protesters were arrested at a rally in Syracuse, N.Y., for blocked traffic by creating a mock Baghdad street scene. Five were arrested In Hartford, Conn., for blocking the front door of a federal courthouse.
• Hsin-Yin Lee and Matthew Cawvey contributed to this article, which is based in part on wire service reports.