TIBURON, Calif. (AP) _ Raymond Thomson, the USAir customer service supervisor who fired a worker linked to the fatal crash of a commuter plane, was a stern, courageous man with a passion for good clothes, friends and neighbors say.

''I can imagine him being challenged by a gunman, and going after him, instead of surrendering,'' said Dorothy Murphy, Thomson's neighbor in the exclusive Marin County community of Tiburon north of San Francisco. She described him as ''like a cowboy.''

Thomson and 42 others died Monday when a Pacific Southwest Airlines commuter plane crashed near San Luis Obispo. Authorities are investigating whether a former USAir employee, 35-year-old David Burke, was gunning for Thomson and caused the airplane to crash by firing a revolver that he smuggled aboard.

Thomson, 48, fired Burke three weeks ago from his customer service job at USAir's office at Los Angeles International Airport, after Burke was accused of stealing company funds.

Thomson was an avid gardener and jogger, maintaining a trim, athletic appearance.

''He wasn't the most outgoing. He usually never waved,'' said Robin Scott, another neighbor. ''He took care of his life in a very personal way.''

Thomson and his wife, American Airlines flight attendant Dorothy Thomson, generally kept to themselves in their pale yellow, $350,000 home which they have occupied for five years. The couple had no children.

Dorothy Thomson declined to speak to reporters. ''She seems physically unable to talk,'' said Tiburon police officer Don Comfort, who was stationed Tuesday at Thomson's house.

Thomson worked for American Airlines as a service manager responsible for about 1,000 employees in San Francisco and San Jose, but left that job in 1980 to become director of public works in Marin County.

Citing personal and domestic reasons, Thomson moved on from the $51,228-a- year government post after two years to go into consulting. ''Ray just got tired of all the politics of the Board of Supervisors,'' neighbor Frank Buchanan said.

In July 1986, Thomson was hired by USAir, commuting between his Tiburon home and his Los Angeles office.

County administrator John Barrows described Thomson as ''pleasant, competent and intelligent,'' and friends said he dressed impeccably in three- piece suits and silk ties. ''He was the best-dressed person in the county building,'' said Lewis Wilson, Marin's acting personnel director.

At least one acquaintance described Thomson as aloof and stern. ''To put it bluntly, he didn't like people who talked back to him,'' said Julius Lucas, chairman of Local 5050 of the Transport Workers Union of American Airlines.

''Ray had a presence, that's what I remember,'' said neighbor Larry Murphy. ''He really fit the pattern of the strong, silent type. He was quiet and confident. There was no bravado about Ray Thomson.''