A Fairfax County family's nanny was shot to death in their home yesterday afternoon while she cared for three children, and police have charged her boyfriend with murder.

Investigators say Earl Ray Scott, 23, of Suitland, was staying with the family temporarily and shot Dena N. Perera, 22, a native of Australia, during an argument.

Neighbors identified the couple who employed Perera as Lowell Martin and Jean Hamilton, both employment counselors in the personnel industry. Three of their children, ages 10, 4 and 15 months, were in the house at the time but weren't injured. In the evening, Chris, the 10-year-old son, was seen watching investigators and television crews on the lawn from an upstairs window.

A police officer who answered the door at the house, in the 8500 block of Electric Avenue in Tysons Woods, near Vienna, said the parents were still trying to calm their children and couldn't comment on the shooting.

Parents on the wooded street of large brick colonials and split-levels called the shooting every working parent's worst fear and said it shocked the block, where several families have nannies.

"If somebody killed the lady, they could have killed the children," said Ghazala Chughtai, a neighbor who provides day care in her home. "It's very scary -- very, very, scary. It's very hard to leave your children with anyone you don't know very well. It's hard to trust."

Perera's body was found in her room in the basement, police said. Police said Scott initially told them the gun went off by accident but changed that explanation after questioning. He was being held without bond on charges of murder and use of a firearm. Police took a handgun they believe was used in the shooting from the house.

Scott called police at 12:45 p.m., investigators said.

That's about 15 minutes after Chughtai said she heard what she thought was a tire exploding. She went outside to look around, didn't see anything and left for the store. When she returned, police were at the house.

The family has lived in the neighborhood for about two years, moving in the spring from another house on the street to the rented two-story colonial where the shooting happened. Besides Chris, neighbors said the family has three other children: Deborah, 22, who doesn't live at the house; a daughter, Laura, 4; and a 15-month-old whose name could not be learned.

"It's just really, really upsetting," said Alia Dajani, a neighbor who employs a nanny to care for her four children. She said she has great trust in the family's nanny but said the shooting was nonetheless "terrifying."

"My kids saw all these police cars and ambulances, and they just were really afraid," she said. "It is Christmastime and all, and I just really feel sick."

Dajani said she didn't know why the nanny's boyfriend was staying at the family's home.

Jim White, standing by his daughter, said an incident such as this strikes fear into any parent who has left a child in someone's care.

"It's a hard thing," he said. "You let these people come into your house. You trust them with your kids."

Another neighbor, David Stauth, said the block of single-family homes usually is quiet.

"It's the first time in over a decade that there has ever been even a break-in, a burglary or a vandalism, as far as I know," Stauth said. "It just goes to show crime can strike in anyone's neighborhood." CAPTION: Susan O'Neill, 29, had cleaned up her drug habit and left the ranks of the homeless.