An 18-year-old Fairfax County man charged in a gang-related machete attack last month faced another accusation of malicious wounding in court yesterday, stemming from the beating and slashing of a former gang member one month earlier.

At a preliminary hearing in Fairfax County General District Court, Judge Robert Smith ruled that police had probable cause to charge Hayner R. Flores with malicious wounding in the April 22 attack. Flores faces the same charge in the May 10 assault in which a 16-year-old boy's hands were mutilated.

The victim of the first assault, Manuel A. Plazaola-Vargas, 19, of Falls Church, testified yesterday that he had just gotten out of his car at a 7-Eleven on Little River Turnpike about 2 a.m. when a man approached him from behind and accused him of being a "snitch" for talking to the police. The voice belonged to Flores, his former friend, he said.

Almost immediately, Plazaola-Vargas said, he was attacked from behind by an assailant who beat him and slashed at his neck, shoulders and ear, causing serious injury.

Plazaola-Vargas said he didn't see the man's face but recognized the clothes -- a black shirt and khaki-colored pants -- as belonging to Flores.

The Fairfax County public defender, Vanessa Antoun, argued that Flores should not be charged because Plazaola-Vargas had not seen his attacker's face and did not know Flores well enough to identify his voice. Smith disagreed and sent the case on to the grand jury.

Police say Flores, 18, is a member of Mara Salvatrucha, or MS-13, believed to be the most violent and largest gang operating in Northern Virginia. He and a youth, who has not been identified because he is a juvenile, have been charged in the May 10 attack on the 16-year-old boy, who police say belonged to a rival gang, Southside Locos. Flores has said he is innocent in that incident.

Flores, a Salvadoran immigrant who lives in Annandale, was present for yesterday's hearing but did not speak. He is being detained at the Fairfax County jail without bond.

In recent years, MS-13 has been linked to at least five killings in Northern Virginia, as well as other shootings, beatings and stabbings.

Police, politicians and community leaders have expressed alarm about the rapid growth of the gang, which is believed to have thousands of followers in the Washington area.