The arrests of about 30 young people on the way to a friend’s wake on Monday have set off a wave of anger in Bushwick, Brooklyn, with more than 50 teenagers assembling yesterday to demand an apology, and their teachers saying that the police had unfairly made a target of the arrested youths — some as young as 13.

But the police defended their actions, saying that a climate of fear and retribution had taken root in the community after more violence erupted in the days after a young gang member was killed.

The police said the man who was killed, Donnell McFarland, 18, was a ranking member of a faction of the Bloods gang in Bushwick. Mr. McFarland was shot to death last week by a teenage rival from a different branch of the gang, the police said.

Classmates and neighborhood friends of the victim gathered at 1:30 p.m. on Monday in a neighborhood park to join what they say was meant to be a solemn trek to the subway station. From there, they planned to take the train to Coney Island, where a wake was being held. Most of the mourners were wearing white T-shirts bearing Mr. McFarland’s image and variations of the words "Rest In Peace" and "Freshh," a nickname for Mr. McFarland.

The police said that members of the local community board had warned them that a faction from the gang would meet in the park that day, that the gathering could turn violent and that rivals would shoot anyone wearing the T-shirts.

As mourners entered the park from all directions and then emerged on Putnam Avenue and headed toward Livingston Street, the police converged and arrested dozens in the group.

"The captain, a high-ranking official in the department, an experienced police captain, made a good-faith judgment and ordered the arrests," said Paul J. Browne, the chief spokesman for the New York Police Department.

One person arrested, Asher Callender, 19, saw it differently. He said the group had simply come together to say goodbye to a friend, and then the police came and cut them off. "They had their guns out. They were cursing at us," he said. "It didn’t matter — children, women, they had us on the fence, up against the wall and on the ground. They treated us like animals."

Mr. Browne responded, "The police did not confront them with guns drawn but they did frisk, which is the standard process before an arrest."

Of the people arrested on Monday, ranging in age from 13 to 22, six females were issued summonses for disorderly conduct and six other people were cited as juveniles. They were released within two hours of their arrests, Mr. Browne said.

The remaining suspects were held overnight and arraigned the next morning on disorderly conduct and unlawful assembly charges. Two of the people were wanted for prior offenses and were still being held yesterday. Most of them have posted bail, Mr. Browne said.

Many of those arrested gathered yesterday inside Make the Road by Walking, a community support organization, on Grove Street. They said that they had never been to jail or handcuffed before, and that the presumption of violence, even gang affiliation, should not have diminished their right to mourn.

"We’re not gang members," said Mr. Callender, a student at Bushwick Community High School. "And there were no gang symbols on the shirts we were wearing. We were just trying to mourn our friend. And they took that from us. We couldn’t even mourn with dignity."

The police said that detectives in the 83rd Precinct have been investigating a gang called the Pretty Boy Family, a branch of the Bloods that operates out of the Hope Garden Housing Project. Its rival, another faction of the Bloods, is the Linden Street Bloods.

Mr. McFarland, who was fatally shot on May 15, was a leader of the Pretty Boy Family, Mr. Browne said. James Kelly, 16, a reputed member of the Linden Street Bloods, has since been charged in the shooting, Mr. Browne said. He added that Mr. McFarland had been feuding with another reputed member of the Linden Street gang at the time of his killing.

The bad blood between the two factions began to boil after the killings.

According to the police, on May 16 a member of the Linden Street set was beaten and stomped. Two days later another member of the gang was beaten and stripped to his underwear.

So, as the group of students, who said they were carrying no weapons or drugs, marched toward the train, they described a swarm of police hopping out of their vehicles, weapons in hand.

"Some of these kids are our leaders," said Brian Favors, a teacher at Bushwick Community High School, which many of the arrested youths attend. "These kids are not gangsters, but you can’t live in the hood and not have a cousin or brother or relative that is associated."

Bushwick Community High School serves students that "no other school in the city wants to take," Mr. Favors said. The students are from 17 to 21, and all have their own stories about how they landed in the school of last chances. But theirs is a school for transformations, Mr. Favors said. There are no metal detectors in the school and only one fight has been reported in four years, he said.

Mark Potashnick, a lawyer for Kumar Singh, one of the people arrested, said the police were positioned and poised to react regardless of how peacefully the mourners behaved.

"It was really an uncalled for event for these kids," he said. "They were going to a friend’s wake, and to be put in jail. It was really uncalled for."

Jerry Schmetterer, the chief spokesman for the district attorney’s office, said the office has opened its own investigation.

"We’ve heard from the community," Mr. Schmetterer added. "And there have been a number of questions to the office as to what happened."

Thomas J. Lueck contributed reporting.