The exact number of arrests was not immediately known, but it was believed between 550 and 650 people were placed in plastic wrist restraints by police and hauled away in buses for a detention center on the outskirts of the city.
"Today in Washington, D.C., the city witnessed shameful police conduct," said Mara Verheyden-Hilliard, co-founder of Partnership for Civil Justice. "We've seen police come out and arrest peaceful demonstrators, trapping and detaining them en masse and without cause.
"We believe that this behavior must stop. They have the right to express their First Amendment rights without being beaten, harassed or arrested."
Friday was the first day of protests that have become a regular feature of the annual meetings of the International Monetary Fund and World Bank by people opposed to their economic policies and capitalism. Other participants included people espousing a myriad of causes.
Anti-war protesters were among those taking to the streets.
The thousands of demonstrators predicted did not materialize, and in most cases police far outnumbered them.
In one instance Friday, several hundred demonstrators were surrounded by truncheon-carrying police and arrested after authorities said the activists refused to follow orders to stop blocking a street just blocks from the White House.
Metropolitan Police Chief Charles Ramsey told United Press International the arrested would be charged with failure to obey police orders and demonstrating without a permit.
"There were folks in the street that were blocking the corner of 14th Street and Pennsylvania Avenue and they refused a police order to disperse," he said. "So we're holding them in the park and bringing them on to buses in an orderly manner. We told them to move and they didn't. So we're moving them ourselves."
Civil rights lawyers observing the protests in Washington said demonstrators were not being given the opportunity to disperse before being taken into custody.
Bystanders and reporters were among those caught up in the sweeps.
As dark descended on the nation's capital, most of the arrested demonstrators were still in custody, said
The lawyer predicted that hundreds of wrongful-arrest complaints would be filed in coming days.
MPD Spokesman Sgt. Joe Gentile had said he expected a minimum of 500 hundred arrests before noon, as police dispersed several different groups of protesters that attempted to shut down streets and disrupt traffic.
Ramsey said no police officers or protesters had been hurt during the arrests to his knowledge.
Capitol Hill Police Chief Terrence Gainer said he was pleased that the protests had been conducted relatively peacefully. He also said there were virtually no disturbances at the Capitol complex his force is responsible for protecting.
"It's as quiet as a Sunday morning at the Capitol," he said. "Earlier this morning, there were about 100 protesters at Union Station (several blocks from the Capitol building) but I was very pleased with how peaceful they were."
Amid the arrests, several reporters and photographers were caught in the sweep by police and detained. United Press International Reporter Stefany Moore was arrested by police and transferred to a central processing facility in Southwest Washington.
A spokesman for the MPD also said about six reporters and photographers for The Washington Post were arrested.
More protests were expected Saturday.