Jean M. Kossarides, 55, chairman of the board and treasurer of the Xebec Corp., a research and development firm in Gaithersburg, and a former military and test pilot, died Wednesday at Suburban Hospital in Bethesda.

An Xebec Corp. spokesman said Mr. Kossarides suffered internal injuries in a commuter bus accident at the airport in Barcelona, Spain, where he had gone on a business trip.

The spokesman said Mr. Kossarides returned here for treatment and had been hospitalized at Suburban Hospital since late March, when the accident occurred.

He had been chairman of the board and treasurer since joining the firm in 1978.

Mr. Kossarides had been president and chief test pilot of Meteor Aero Inc., a Gaithersburg company he founded in 1955, which was said to be the first approved for independent flight testing of military infrared reconnaissance and advanced navigation equipment.

He was a longtime member of the Society of Experimental Test Pilots and remained current in a number of high-performance aircraft.

A former Air Force colonel, he was a fighter pilot in the Army Air Corps in Europe during World War ii, and saw combat during the Korean conflict.

His military decorations included the Distinguished Flying Cross with oak leaf cluster, the Purple Heart, the French Medale Militaire and the French Croix de Guerre.

Since 1970, he had been a technical consultant to the Applied Physics Laboratory of Johns Hopkins University and to major aerospace corporations.

He was formerly associated with JMK Inc., a Gaithersburg aviation and aerospace consulting firm, Sperry Rand, Martin Marietta, IT&T and Control Data Corporation.

Mr. Kossarides was born in Cliffside Park, N.J., and earned a bachelor's degree in business education from New Jersey State College. He lived in Gaithersburg.

He was active in the Air Force Association, the Navy League, the Association of Naval Aviation and the P-40 Warhawks Pilots Association and P-47 Thunderbolt Pilots Association. He was a member of the Fairfax Hunt Club and the Woodlawn Polo and Riding Club.

Survivors include his wife, the former June Pulcer, and a daughter, Desiree M., both of Gaithersburg; a son, Jean Jr., of Los Angeles, and his mother, Susan Kossarides of Miami.