A Fairfax County man who apparently tried to intervene in a fight between two groups of teenagers was shot to death Monday night, and police said a 17-year-old was arrested yesterday and charged with murder.

Henry J. Andrade, a 26-year-old father of two young girls, was outside his home in the 2300 block of Fort Drive in the Huntington area about 11:30 p.m. Police said two groups of teenagers, who had argued earlier in the day, converged.

A witness to the shooting, who asked to remain anonymous for safety reasons, said Andrade was simply trying to defend a neighborhood teen. Andrade was standing with three other people, then approached a group of four young men and was shot once in the chest, police said.

"He was just trying to be a good person and help a friend out," the witness said. "All he did was try to stick up for his friend, because he didn't want nothing bad to happen to him. Then he's the one that ended up getting shot."

The four young men ran away.

Witnesses provided information about the suspected shooter, and he was arrested at his home about 8 a.m. yesterday, police spokeswoman Mary Mulrenan said. His name was not released because he is a juvenile.

He was charged in juvenile court with murder and use of a firearm during a felony, and he was being held in the Fairfax juvenile jail last night. The incident was not gang-related, police said.

Andrade's family said he was merely acting as a peacemaker between the two groups, but Mulrenan said detectives had not determined that yesterday. "We're still trying to sort that out," she said.

Andrade's death was the 15th slaying in Fairfax this year, five more than last year or 2003.

Andrade worked as a service adviser at Ourisman Dodge in the Huntington area and had previously worked there as a mechanic, his longtime girlfriend, Sandra Flores, 25, said yesterday. The couple lived with their daughters, 9 and 5, and Andrade's parents.

His parents are from El Salvador, Flores said, but Andrade was born in the United States and grew up in Northern Virginia.