A Fairfax County jail prisoner being treated at a private doctor's office overpowered a deputy sheriff yesterday, took his gun, commandeered a car in Fairfax City and was free for about 40 minutes before being recaptured by Fairfax County police near the Capital Beltway.

Carl Peed, chief deputy sheriff, said it was the first time he could recall a deputy being overpowered and disarmed by a prisoner.

Peed and Fairfax City police spokesman Tom Welle gave this account:

Larry Cash, 31, of Rockville, who was awaiting transfer to prison to serve a burglary term, was taken by a deputy to the office of a pulmonary specialist at 9926 Main St. in Fairfax City for examination about 11:30 yesterday morning. His handcuffs had been taken off so his chest could be X-rayed.

"As the deputy went to put the cuffs back on," Peed said, "he hit the deputy, took his weapon, hit him upside the head with the gun, and escaped."

Outside, Cash opened the passenger door of a car stopped at a red light at Main Street and Burke Station Road and hopped in.

"A large man, whom I noticed standing on a nearby corner, jumped in my car and I jumped out," said Jerold Lindsey, 41, the owner of the car. "I was not going to fight him for the car. He was a big guy."

A motorist saw Lindsey's car being taken and followed it.

Cash drove down Main Street (Rte. 236) and abandoned the car at Wakefield Park near the Beltway. The motorist called police and told them of the car's whereabouts.

A dozen county police officers converged on the park and recaptured Cash about 12:15 p.m. The deputy's Smith and Wesson .38-caliber revolver was found in the car.

Peed refused to identify the deputy, a 14-year veteran, who he said was treated for abrasions at Commonwealth Hospital and released. The deputy was placed on routine administrative leave while the sheriff's department investigates "to see if there were policies or procedures that were not followed," Peed said.

Cash had been convicted on two counts of burglary and was awaiting transfer to Powhatan Correctional Center west of Richmond to serve a 12-year sentence. He was charged with escape, assault on a law enforcement official, malicious wounding and robbery, and was returned to the jail, authorities said.