A security guard at Gar-Field Senior High School was arrested yesterday on charges that he filed a false police report about an alleged attack in late December.

Robert Ellis Brown, 66, of Dale City, falsely told police that he had been hit on the head by a burglar while making his rounds of the school Dec. 23, Prince William County police said. Brown told police that he was knocked down by an unidentified person while checking the school's hallways, part of his regular duties, according to police.

Sgt. Kim Chinn, police spokeswoman, said yesterday that detectives determined Brown had lied to cover up the fact that he had fallen while alone in the building.

"During the investigation, we learned that what really happened is that he had fallen and hit his head," Chinn said. "He was concerned that he might lose this position because people might think he was too old or maybe wasn't competent or able to do his job."

Chinn said Brown, who lives on school grounds as part of his job, was worried that he would be fired and lose his living quarters if officials learned that he had fallen while on duty. Brown was arrested yesterday and charged with one count of filing a false police report. He was released without bond and is scheduled to appear in court Feb. 4.

Chinn said false reports to the police are treated as serious criminal offenses. If convicted, Brown could be sentenced to up to one year in prison and fined up to $2,500.

"These cases, as always, cause us to spend a lot of time and taxpayer money," Chinn said. "It is very serious when people falsely call the police."