The father of the Salvadoran immigrant accused in a machete attack on a Fairfax County teenager said yesterday that he had tried to warn authorities that his son was a gang member and should receive help but was frustrated in his efforts.

"I told them I needed help, that he was getting into bad things," said Rigoberto Hernandez, 42, father of Hayner R. Flores, 18, who was charged last week with malicious wounding and participation in a gang in the assault on the 16-year-old.

Hernandez said he had complained to the judge and police who were dealing with his son for truancy problems over a year ago. Hernandez had hoped that they could commit his son to a reform school.

Fairfax County police spokeswoman Mary Ann Jennings said police are investigating the May 10 assault, which occurred in the 6400 block of Edsall Road. All four fingers on the victim's left hand were cut off, and his right hand was nearly severed.

In what police say was an unrelated gang attack in Herndon on Sunday night, Jose Sandoval, 17, a Herndon High School freshman, was shot and killed by an assailant riding a bike while he was walking on a quiet street near the Washington & Old Dominion trail. Law enforcement sources said the person who shot Sandoval and a 16-year-old girl who was with him had an "MS" gang tattoo on his forehead. "MS" stands for Mara Salvatrucha, or MS-13.

No arrests have been made, and the girl, who was shot in the back, is in stable condition, police said.

The recent gang-related attacks in Northern Virginia have alarmed community members and officials. The four U.S. senators from Maryland and Virginia have written a letter to Attorney General John D. Ashcroft urging him to assist authorities in the Washington region, according to a statement released yesterday by Maryland Sen. Paul S. Sarbanes (D).

Police said the machete attack was part of a feud between MS and the victim's gang, South Side Locos, or SSL. Flores, a reputed MS member, has proclaimed his innocence through an attorney, Hernandez said.

Flores, who is being held at the Fairfax County Adult Detention Center, grew up mostly in El Salvador and came to the United States illegally three years ago, Hernandez said.

Hernandez said he and the youth's mother were thrilled when the boy arrived in Virginia. The couple have had three more children since moving here.

"The first days were great, really great," he said. "Afterward, there were problems and problems and problems."

After about a year at Annandale High School, he said, Flores started skipping class. Hernandez said he and his wife were unable to change their son's behavior, and he was eventually suspended from school.

By then, Hernandez had recognized that his son sported a tattoo, signifying membership in MS-13. He said he didn't know his son's fellow gang members but had heard that his son's gang nickname was "Spike."

His son was detained twice for brief periods because he did not show up to attend court dates, Hernandez said. His last hearing was before his 18th birthday, in March, he said.

"I feel badly, and his mother too," Hernandez said.