-- One late August evening, Alexander Pincus pedaled his bicycle to the Second Avenue Deli to buy matzo ball soup, a pastrami-on-rye and potato latkes for his sweetheart, who was sick with a cold.

He would not return for 28 hours. As Pincus and a friend left the deli, they inadvertently walked into a police blockade and sweep of bicycle-riding protesters two days before the Republican National Convention began. "I asked an officer how I could get home," Pincus recalled. "He said, 'Follow me,' and we went a few feet and cops grabbed us. They handcuffed us and made us kneel for an hour."

Police carted Pincus to a holding cell topped with razor wire and held him for 25 hours without access to a lawyer. The floor was a soup of oil and soot, he said, and the cell had so few portable toilets that some people relieved themselves in the corner. Pincus said a shoulder was dislocated as police pulled back his arms to handcuff him. "Cops kept saying to us, 'This is what you get for protesting,' " said Pincus, whose account of his arrest is supported in part by deli workers and a time-stamped food receipt.

Pincus was one of 1,821 people arrested in police sweeps before and during the Republican convention, the largest number of arrests associated with any American major-party convention. At the Democratic convention in Chicago in 1968, which unlike New York's was marked by widespread police brutality, cops made fewer than 700 arrests.

In the days after the convention, Mayor Michael R. Bloomberg and Police Commissioner Raymond Kelly stated that "every NYPD officer did a great job." But interviews with state court officials, City Council representatives, prosecutors, protesters and civil libertarians -- and a review of videos of demonstrations -- point to many problems with the police performance. Officers often sealed off streets with orange netting and used motor scooters and horses to sweep up hundreds of protesters at a time, including many who appear to have broken no laws. In two cases, police commanders appeared to allow marches to proceed, only to order many arrests minutes later.

Most of those arrested were held for more than two days without being arraigned, which a state Supreme Court judge ruled was a violation of legal guidelines. Defense attorneys predict a flood of civil lawsuits once protesters have settled the misdemeanor charges lodged against them.

"The overriding problem during the convention was the indiscriminate arrests . . . of people who did nothing wrong," Donna Lieberman, executive director of the New York Civil Liberties Union, said at a City Council hearing last week. "They were arrested because they were . . . participating in a lawful demonstration."

Police officials declined to talk about these problems last week, citing a pending court case. But the city's criminal justice coordinator, John Feinblatt, said in an interview that city lawyers tried to weed out the unjustly arrested and that the volume of arrests -- more than 1,100 on one day -- overwhelmed the police department. More broadly, Bloomberg and Kelly defended the vast majority of the arrests as justified and described holding cells as clean and humane.

Bloomberg, in interviews during convention week, said that protesters expected prisons to look like "Club Med." Kelly said police encountered other delays as they tried to find separate cells for a large number of female detainees.

The first mass arrests came three days before the Aug. 30 to Sept. 2 convention, when police swooped down on Critical Mass, a loosely knit collective of bicyclists who periodically flood city streets and slow traffic. Police usually tolerate the disruption, but that night officers arrested more than 200. Kelly told New York magazine that he wanted to send protesters a message.

The next few days were quiet, and a quarter-million-strong march went forward Aug. 29 without incident.

But the mood changed Aug. 31, when police made 1,128 arrests. Anarchists had pledged a day of resistance, blocking traffic. Police arrested hundreds, and civil liberties lawyers on the scene described most arrests as lawful.

But farther downtown on the same day, the War Resisters League, a decades-old pacifist group, was readying a peaceful march from Ground Zero to Madison Square Garden, where it intended to conduct a civil disobedience "die in."

A video provided by the New York Civil Liberties Union shows police commanders laying out the ground rules: As long as protesters did not block traffic, they would not get arrested during the walk north. (No permit is required for a march on a sidewalk as long as protesters leave space for other pedestrians to pass.) Within a block or two, however, the video shows marchers lined up on the sidewalk, far from an intersection, as a police officer announces on a bullhorn: "You're under arrest."

"They came with batons, bicycles, they came with netting," said the Rev. G. Simon Harak, a Jesuit priest. "The kind of forces you expect to be turned on terrorists was unleashed on us."

Police arrested 200 people, saying they had blocked the sidewalk.

About the same time Tuesday, several other groups of protesters started walking two abreast from Union Square, the city's historic protest soapbox, to Madison Square Garden. However, several demonstrators say -- and photographs show -- that police soon stopped them, asked them to raise their hands and arrested them.

Throughout the week, police also picked up dozens of people who appeared to have nothing to do with demonstrations, the New York Civil Liberties Union said. Among those swept up by police were several newspaper reporters, two women shopping at the Gap, a feeder company executive out for dinner with a friend, and Wendy Stefanelli, a costume designer with the TV show "Sex and the City," who was walking to get a drink with a friend.

She saw a police officer pushing a demonstrator against a wall and asked him to lay off. Police flooded the street, and she was arrested. "I don't know how this could happen," Stefanelli, 35, told the City Council last week. "I was coming from work."

Bloomberg has acknowledged that police may have arrested some innocent bystanders, but he suggested that it was partly their fault.

"If you go to where people are protesting and don't want to be part of the protest, you're always going to run the risk that maybe you'll get tied up with it," he said on a weekly radio show on WABC.

Police hauled those arrested to newly built holding cells in a former bus depot on the Hudson River. In interviews, two dozen protesters from six states described floors covered in oil and officers who denied access to family and lawyers.

During this time, Deputy Police Commissioner Paul J. Browne twice stated to The Washington Post that most protesters had been released after six or seven hours. Only on Thursday, the last day of the convention, did he acknowledge the much longer delays.

Last Friday, Feinblatt, the city's criminal justice coordinator, attributed the problems to a glut of arrests. Other city officials have spoken of state delays in processing fingerprints.

But senior police officials had said for months that they anticipated 1,000 arrests a day during the convention. Citing such warnings, state court officials, prosecutors and Legal Aid lawyers doubled staffing and opened extra courtrooms during convention week.

"What happened for several days is that we had resources available and we simply were not getting the bodies produced, the defendants in the courtroom," said David Bookstaver, spokesman for the state office of court administration.

State officials also released figures showing that they had processed 94 percent of all fingerprints within one hour.

The backlog created a legal crisis for the city. State Supreme Court Judge John Cataldo held officials in contempt of court. "These people," Cataldo said of those arrested, "have already been victims of the process."

His order resulted in the release of almost 500 people. Tricia Schriefer of Milwaukee had spent two days trying to find her daughter, Claire, 19, a college student who had been arrested Aug. 31. Tricia Schriefer called the police and city offices, only to be told that her daughter was in a legal twilight.

Her daughter was finally released -- without charges -- after Cataldo issued his ruling. "To be held for 50 hours and not be charged . . . it's pretty outrageous," Schriefer said. "It's just counter to everything I had understood about our legal process."

Since the convention ended, protesters have flocked daily into Manhattan Criminal Court, where most of them are accepting misdemeanors and violations -- charges that would typically carry no jail term. The difference between them and someone caught double-parking is that the protesters already had spent two days in jail.

"Too many New Yorkers were willing to look away," said Norman Siegal, a civil liberties lawyer who is representing Pincus. "We don't lose our rights overnight with a big bang; we lose them incrementally over time."

Alexander Pincus was arrested as he was leaving a deli.