Not long before she was to take the stage, the 17-year-old keyboardist in the go-go band Drastic Measures left the packed gymnasium in Langley Park and walked out into the warm night air.

She returned a few minutes later, carried by a friend and bleeding from a gash on the left side of her neck, a witness said. She was attacked before 9 p.m. Friday with a sharp instrument, police said, by a group of Latino youths in a community center parking lot a couple of hundred yards from where seven security guards and three Prince George's County police officers were keeping watch over the back-to-school teen concert.

The Maryland-National Capital Park Police said they did not know whether the slashing was the work of the violent Latino gang Mara Salvatrucha, or MS-13, whose members have been accused of a series of stabbings and slashings in Montgomery County in recent days. The slasher is believed to be a Latino juvenile, said Lt. Stanley Johnson, the park police spokesman. "It very well could be" gang-related, he said.

The attack came two days after three Latino immigrants had their throats slashed in the parking lot of a Toys R Us store in Langley Park. Detectives investigating the attacks, which killed two of the men, have some leads but have not identified any suspects, said a Prince George's County investigator who did not want to be identified because the case is still open. He said he believed the stabbing of the girl was not connected with the homicides.

Residents said the neighborhood has become increasingly violent and a gathering place for increasingly brazen and intimidating gang members.

"This is getting crazy over here," said Jose Ramos, 33, who lives across the street from the community center, heard the shouting and saw part of the fight. About a month ago, Ramos said, he watched as two men lay bleeding from stab wounds directly across the street from his porch. "We've never had so much trouble as in the past year," he said.

The girl, whom police did not name, walked outside with about three other people, perhaps to get musical equipment, said Chrissy Dixon, who helps organize the weekly concerts at the Langley Park Boys and Girls Club. Police said the group of black teens got involved in an argument with about eight Latino youth and a fight ensued.

The girl was taken to the Washington Hospital Center, where she underwent surgery for more than two hours and was in stable condition last night, Johnson said.

The Friday night concerts, which began in May, attract about 400 teens each week and are intended to be "nonviolent, non-alcohol, peaceful" events, said Julie Moses, president of the Langley Park Boys and Girls Club. Security has been a high priority, with the shows staffed by guards and monitored by police. After paying a $3 cover charge, the teens are not supposed to leave the building until after the concert. As a band member, the girl was given an orange wristband so she could come and go.

The police presence was to be enhanced for a concert planned for last night, Dixon said. Moses said she will hold a rally Aug. 18 outside the club, condemning the violence.

"I know these kids are terrified around here" of MS-13, Moses said. "We have to drop them off at home because they're afraid to walk."

A 13-year-old boy who attended the concert and lives in the neighborhood said he frequently sees young men who he thinks are MS-13 members, sometimes identifiable by their long belts hanging down, blue jerseys with the number 13 and shaved heads.

He said he was walking home late at night about two weeks ago when a large group of youths he believes were in MS-13 approached him, one of them wielding a long knife.

"They said, 'Yo, what you claimin', what you represent?' " said the boy, who asked to remain anonymous for fear of retaliation. "I said, 'I don't represent nothing, man.' . . . I was running for my life."

The increased visibility of gang members has unnerved adults as well. Ramos said he moved to Langley Park five years ago from his home east of Los Angeles to avoid the gang violence there. Now he's afraid to take his two young daughters to a nearby park because it has become the territory of MS-13.

"The police are going to have to do something to stop this," he said.

Staff writer Allison Klein contributed to this report.