The owner of an Alexandria record store filed suit against a Roman Catholic bishop yesterday, claiming that employes of a parochial school falsely warned students against patronizing the store because illegal drugs were sold there.

Clyde Ross Sr., owner of the Psychedelic Record Shack, 3810 Mount Vernon Ave., seeks $100,000 in his damage suit against the Most Rev. Thomas J. Welsh, spiritual leader of Catholics in the Diocese of Arlington which includes Northern Virginia.

The suit, filed in U.S. District Court in Alexandria, claims that "certain administrators and employes" of St. Rita's School, 3801 Russell Rd., Alexandria sent notes home with students saying the record shop was "off limits... because narcotics were being sold" there.

From Sept. 1, 1977, to Nov. 28, 1978, while the parents were receiving the notes from school officials, they were also being told that the record store was off limits because, in addition to the alleged drug sales, it had also been raided by the Alexandria police, the suit states.

The suit contends that drugs sales never took place there, and that the police have never raided the store, located a block from the school.

Welsh was sued in his capacity as bishop of the diocese, which owns St. Rita's School. Although he is the only defendant his name does not appear in the text of the complaint.

An assistant at Welsh's office said yesterday that Welsh was out of town and could not be reached for comment. Telephone calls to the school went unanswered.

The written notes and statements were the "direct" cause of declining sales at the store, according to the suit. Ross, who has owned the store for seven years, declined comment yesterday.

James C. Clark Ross's attorney said he didn't have any of the notes sent home with the children, although he said he was in possession of an "apology" sent by the school administrators to parents late last year. He declined to elaborate.

St. Rita's School teaches about 400 students from the first through the eighth grades, and charges a tuition of about $300 annually, according to the parent of a student there. The school was opened by the Arlington diocese in the late 1940s, the parent said.