A Montgomery County Circuit Court jury yesterday rejected a $6.5 million suit brought by the parents of a Kensington hairdresser who was fatally shot in 1982 by an off-duty Montgomery County policeman.

After a week of testimony, the panel found in favor of Bruce L. Jackson of Gaithersburg, who now is an insurance agent. In the fall of 1982, a police review board fired Jackson, then a 9 1/2-year police veteran, after charging him with lying to police investigators and neglect of duty stemming from the Feb. 11, 1982 fatal shooting of Jan Michael Moore.

A county grand jury also investigated the slaying, but did not press criminal charges against Jackson, according to his attorney, Allen Katz.

Moore's parents, Katherine L. Wilson of Cumberland and Jack F. Moore of Las Vegas, filed the civil suit accusing Jackson, 39, of assault, battery and negligence and of depriving Moore of his civil rights.

According to trial testimony, Jackson was off duty and had been drinking beer in the District of Columbia. As he drove home he saw a man get out of a car at the intersection of Wisconsin Avenue and Bradley Blvd., approach another motorist in a car, kick the bumper and curse and yell at the people inside.

Jackson testified that he yelled at the man to leave the people inside alone. The man, later identified as Moore, got back into his car and continued driving north. Jackson followed, got out of his car and approached Moore at East West Highway, according to his testimony. Moore drew a knife and Jackson, an undercover officer who was not in uniform, shot him through the car window, according to testimony.