A Manhattan Criminal Court judge ruled yesterday that the city was holding approximately 500 prisoners illegally and fined the city hundreds of thousands of dollars when the detainees were not released in compliance with his order.

The illegal detainees represent a fraction of the approximately 1,800 people arrested in connection with the Republican National Convention.

Judge John Cataldo’s ruling applied to detainees held for at least 36 hours and was in response to a writ of habeas corpus issued by attorneys Norman Siegel and members of the National Lawyers Guild.

Mr. Siegel hailed the judge’s decision a victory and said it opens the possibility for lawsuits against the city by people who were illegally detained. Mr. Siegel, however, said the fight wasn’t over until hundreds of detainees who were “missing in the system” were identified and released.

“The family doesn’t know the circumstances of his arrest, or where he is,” said Mr. Siegel in reference to his 17-year old client, Richard Prince. “The family has been in the dark.”

Corporation Counsel Michael Cardoza objected that the judge’s decision did not take into account the difficulties of processing the large numbers of prisoners caused by the protests.

“The judge was wrong not to permit the city sufficient time to complete the processing of arrestees,” said Mr. Cardoza in a written statement. “The high number of arrests was the result of the concerted efforts of many groups throughout the city to stop traffic, obstruct the movement of others, and interfere with the normal activities of New Yorkers. The release of those individuals is unfortunate to say the least.”

Judge Cataldo issued his ruling at about 4 p.m. and ordered that prisoners held at least 36 hours be released by 5 p.m. After 6 p.m., when most of the specified prisoners were still in custody, the judge fined the city for being in contempt of court. The exact amount of the fine and the exact number of prisoners affected will be determined next week, said Judge Cataldo, who noted that some prisoners were held for more than 65 hours.

Mr. Cardoza told the judge that releasing hundreds of prisoners in such a short time simply wasn’t possible, because the prisoners who conformed to the judge’s ruling had to be identified among the prisoners who did not apply.

In a televised interview less than two hours after the judge’s contempt of court ruling, Police Commissioner Raymond Kelly said that all but about 100 of the specified prisoners had been released.

“The system was overwhelmed, there’s no question about it,” said Mr. Kelly, who said the process was slowed by the fact that 65% of the detainees are from out of state.

Mr. Cardoza said the city typically processes between 250 and 300 arrests daily, but that tally quadrupled on Tuesday, “making it impossible to process them all on time,” despite the implementation of special processing centers against “the possibility of a large number of arrests.”

Mr. Siegel said that most of the detainees are accused of disorderly conduct, a violation, but charges would not be brought against those who were released under the judge’s orders.

“Even if they had been convicted of the disorderly conduct charge, they wouldn’t have gotten two days in jail, anyway,” said Mr. Siegel.

The writ of habeas corpus included a claim that arrested protesters would be detained until the Republican National Convention ended Thursday night.

“The city’s plan was by design to keep the protesters detained until President Bush left the city of New York,” said Mr. Siegel.

According to the writ, this claim was based on a telephone conversation between a woman who was trying to track down her detained son’s whereabouts and a worker at Central Booking who allegedly said, “All of the demonstrators would be held until after President Bush left town.” Police officials flatly denied any such claims, which they blamed on a fraudulent memo circulated by the National Lawyers Guild.

In the morning, more than 100 protesters hung banners in Grand Central Terminal. After one man standing in the middle of the Great Hall blew a whistle, activists wearing black T-shirts and chanting “Fight AIDS, not Iraq!” streamed from hallways and ticket lines to form a perimeter around the concourse. They held up signs and banners, the largest of which read “America has AIDS, our next president must stop the plague,” until police officers arrived. Most of the protesters fled, but 19 were arrested.

Last night, protesters rallied near Madison Square Garden and held a candlelight vigil in Union Square to call for an end to the Bush presidency one last time.

A few thousand edgy and exhausted protesters packed three blocks of Eighth Avenue south of 31st Street as the Answer Coalition. Police officers placed pens around each block, barring groups of protesters from moving forward toward a makeshift stage that had been set up for Answer speakers. Tempers flared, giving rise to anti-police officer chants and demands to be allowed to move forward.

At Union Square a patchwork of groups with ideologies ranging from anarchy to socialism to mere anti-Bushism held a candlelight vigil that stood as a kind of closing ceremony to a week of anti-Republican protest. A few of the several hundred individuals in the square listened to orations and others chanted in groups, but the only moment of unity came when everyone joined in a chorus of boos for a Fox News van stopped at a light on Broadway.

“I hope we’ve made a difference,” said a protester from Tampa, Susan Smith, who came to New York to protest the GOP agenda. “I’m tired and now I’ve got to get home to a hurricane.”