Lawyers for New York City asked a federal judge on Thursday to dismiss dozens of lawsuits filed against the city by hundreds of people who contend they were falsely arrested during the 2004 Republican National Convention in Manhattan.

Nearly eight years ago, protesters objected that the police in New York had conducted mass arrests and held people for long periods in miserable conditions on a West Side pier. They also claimed that the city had discriminated against those arrested in connection with the convention by not simply giving summonses to people accused of minor offenses that would normally be dealt with in that manner.

Arguments on the city’s motion before Judge Richard J. Sullivan of Federal District Court in Manhattan dealt with two high-profile mass arrests. One event, organized by the War Resisters League, involved more than 200 people who were arrested near Fulton Street minutes after embarking on a sidewalk march. Later on the same day, after an impromptu street performance by marching bands, the police cordoned off a block of 16th Street just east of Union Square and arrested hundreds more.

In a memorandum, lawyers for the city said that the arrests were permissible because “where it reasonably appears to the police that a large group is engaging in unlawful conduct, the police have probable cause to arrest the entire group.” For instance, the city’s lawyers said, protesters on Fulton Street had marched on the sidewalk without a city permit and had violated directives from the police to walk two abreast, with some crossing a street against a light.