A former Fairfax County police officer who was fired for selling his privately owned gun to a friend sued the department yesterday, alleging the termination violated his constitutional right to choose his acquaintances.

Paulo Freyesleben, with the force for 10 years, said he was told by his commander, Audrey Slyman, that he was dismissed because he sold the gun and some ammunition to "a young man who looked like a gang member," according to a four-page complaint filed in U.S. District Court in Alexandria.

Freyesleben's conduct violated police policy and was "unbecoming" for an officer, Police Chief J. Thomas Manger ruled in April 1998, the complaint said.

The gun sale was legal and the gun buyer was not a gang member and did not have a criminal record, said Richard Gardiner, Freyesleben's attorney. He said Freyesleben befriended the young man while providing security at a McDonald's.

Lt. Amy Lubas, a Fairfax police spokeswoman, said, "We have not been notified of this lawsuit and therefore we cannot respond to it."

According to the records of the Fairfax Civil Service Commission, Freyesleben sold the 9mm Smith & Wesson to a man he had met only three or four times and knew only as "Mario." The commission also found that Freyesleben also sold him a box of ammunition issued by the Fairfax County Police Department firing range that was labeled "for law enforcement purposes only." According to the commission, Freyesleben delivered the ammunition to the buyer while on duty, in uniform and driving a police car.

In its four-page report upholding the firing, the commission ruled that "Freyesleben's handling of this entire matter fell well below the standards of responsible behavior and exercise of discretion that must be expected of a Fairfax County police officer."

Gardiner said that the ammunition was not county property and that Freyesleben had gotten to know the gun buyer before the sale. Fairfax learned about the sale when the young man talked about the transaction to another police officer.

"They're punishing him because he chose to associate with someone who looked like a gang member," Gardiner said.