A 16-year-old Centreville youth was arrested yesterday after allegedly firing a pellet gun at a 10-year-old girl on the playground of her Fairfax County elementary school Friday.

Fairfax County police said that no one was hit by the BB shot and that none of the children on the playground reported the incident at the time. When the 16-year-old appeared at Westlawn Elementary School again Monday, officials were notified. Even as police investigated, the teenager visited the school a third time, on Tuesday.

Police charged the teenager yesterday with one count of reckless discharge of a firearm within 1,000 feet of a school, which is a felony, and three misdemeanor counts of trespassing. The youth, who was not identified because of his age, was being held last night in the Fairfax juvenile detention center.

School officials said none of the children who witnessed Friday's incident informed an adult. Westlawn Principal Jean Hall said she learned of it Monday from a concerned parent who had heard the story from her child over the weekend. Hall then contacted county police and school security officers.

The teenage boy is a former neighbor of the girl, but police say they do not know why he allegedly confronted her three times. The youth was first seen on the school's roof Friday and later was observed standing behind a fence near the playground. He allegedly fired at least one shot at the girl, with other children nearby, police spokeswoman Gretchen Lacharite said.

Some Westlawn parents were critical of school officials for not moving more quickly to get out word about what had happened.

But Westlawn PTA President Mary Van Wijngaarden said Hall was quick to inform parents once information became available. She said Hall addressed the PTA board at its regular meeting Monday and told them what she knew at that time.

Fairfax schools spokeswoman Kitty Porterfield said that officials did not want to put out any information without having all the facts and that police spent Monday afternoon and much of Tuesday interviewing students. "Based on initial reports, they thought they were simply looking at a case of an older student hanging about the school yard and a possible case of vandalism," Porterfield said, referring to some fresh graffiti on the school's roof. "If you jump the gun on these things, you risk putting wrong information out there and damaging the police investigation."

Porterfield said Hall has met with the children who are believed to have witnessed Friday's incident and has advised her teachers to speak with their students about reporting suspicious events promptly. A letter went home to Westlawn parents yesterday informing them of the incident and reminding them to review safety precautions with their children.

Fairfax police and school security officers will have a heightened presence at the school for several days, Porterfield said.

In addition to the firearms and trespassing charges, the teenager faces disciplinary action at school, such as suspension or possibly expulsion.