The streets of Crown Heights, Brooklyn, resembled an armed camp on Wednesday.

On Albany Avenue, near where a black man was assaulted by Hasidic Jews last month, police officers milled around a mobile command center. Two blocks farther down Albany, at the corner where a Jewish teenager was robbed and beaten by black youths last week, an officer stood watch. Marked police cars have been following yeshiva school buses since last week, when black children threw rocks through the windows of a bus full of Hasidic toddlers.

On Eastern Parkway, officers peered down from a crane and scanned the horizon from a rooftop for signs of trouble.

Along the wide streets lined with splendid brownstones and brick apartment buildings in one of the city’s most vibrantly multiethnic neighborhoods, officers from at least 10 precincts stood on corners, studied maps of unfamiliar territory and handed report logs to plainclothes colleagues in unmarked sport utility vehicles.

Crown Heights is flaring up again, as it has every so often since the 1991 racial unrest that erupted after a 7-year-old black boy was fatally struck by a Hasidic driver. The violence also left a Jewish man dead.

As always, there are complicating factors. A Jewish man wanted for questioning in the assault of the black man is a member of a civilian patrol group that has often been criticized for its tactics; the authorities say his friends and colleagues have been uncooperative with the police’s efforts to find him. The assault victim is the son of a police officer.

The Brooklyn district attorney, Charles J. Hynes, has been criticized by Jews for convening an investigative grand jury, a rare step, to look into the assault. The police have been taken to task by black residents for their failure to track down the potential suspect. Mr. Hynes has inflamed passions in some quarters by comparing the Jewish civilian patrol group, the Shmira, to the Bloods and the Crips. Jews say the police are slow to respond to assaults against them and even slower to solve the crimes. Blacks say the police pay more attention to crimes against Jews than against blacks.

Though violent crime in the 71st Precinct, which includes the predominantly Jewish part of Crown Heights, is falling this year, as it has pretty much every year since the early 1990s, bias crimes are up. There have been nine recorded so far this year, compared with seven at this time last year.

Tempers are short, people are confused, and there seems to be no consensus on what to do.

“I think there is a problem,” said Rabbi Menachem Posner, an active member of the community. “The question is exactly what the problem is.”

Black and Jewish community leaders are meeting and preaching cooperation and communication, but for now, the Police Department, ever mindful of the specter of 1991, is taking no chances. Its massive show of force in the neighborhood began on Tuesday and will continue indefinitely, said Paul J. Browne, the department’s chief spokesman.

“Crime generally is down,” Mr. Browne said, “but because of the recent tensions, we’ve increased police visibility to lessen them.”

The current problems in Crown Heights began in the late afternoon of April 14, when a 20-year-old black man, Andrew Charles, the son of a New York City police officer, was walking with a black friend and they exchanged stares and possibly words with two young white men, according to the police. One of the white men sprayed Mr. Charles with Mace or pepper spray, the police said. When Mr. Charles ran, the authorities said, an S.U.V. pulled up and a white passenger jumped out and hit him with a stick. The attack was deemed a bias crime because “every other possible motive has been excluded,” a law enforcement official said.

Law enforcement officials said that the attack was linked to members of the Shmira, and that the group was not cooperating with the investigation.

“You can’t have a group, whether it’s the Bloods, Crips or Shmira, acting like vigilantes,” Mr. Hynes said.

Click HERE to read the extended article on the NY Times website.