The lawsuit filed in Manhattan federal court charged the NYPD "unlawfully arrested peaceful protesters and detained them for excessively long periods" after the April 7, 2003, rally outside an investment bank they accused of war profiteering.

A spokeswoman for the city's law department said counsel had not yet read the legal papers, but "will be reviewing them thoroughly" when they do.

Center for Constitutional Rights lawyers said their lawsuit, which charged the police with violating free speech rights, was also filed with an eye to demonstrations planned for the Republican National Convention in New York in August.

"We believe these arrests and detentions were part of a nationwide pattern ... a concerted effort to keep people off the streets and deter people who would protest from coming out," lawyer Nancy Chang said.

"We don't want to live in a country where people do not feel free to express themselves," Chang said.

The suit was filed a day after U.S. prosecutors in Iowa dropped subpoenas issued last week ordering anti-war activists to testify before a grand jury. Under pressure from civil liberties advocates, a subpoena was also withdrawn on Drake University to provide information on a campus anti-war forum.

Chang said civil rights groups had filed lawsuits against authorities over police handling of anti-war rallies in cities such as Oakland, California, Washington and Seattle.

CIVIL LIBERTIES DEBATE

These and other cases are part of a raging debate over civil liberties as the Bush administration fights its war on terrorism following the Sept. 11, 2001, attacks on America. Law enforcement officials, free speech advocates and courts have all acknowledged the attacks and the U.S. war on Iraq created a different atmosphere for policing and security.

At the April demonstration in New York, an ad hoc group of activists called "M27 Coalition" rallied outside an affiliate of the Carlyle Group, which has ties to the defense industry.

Officers arrested the activists, who said they followed police guidelines for the sidewalk demonstration. Some were held for up to 12 hours, but disorderly conduct charges were dismissed against the 52 named in Wednesday's lawsuit.

The lawsuit seeks unspecified monetary compensation and a declaration that police actions were "retaliatory and unconstitutional."

New York activists organized one of the largest anti-war demonstrations on Feb. 15, 2003, when hundreds of thousands took to the streets five weeks before the U.S. and British invasion of Iraq over its purported stockpiles of weapons of mass destruction. No weapons stockpiles have been found.