The Food and Drug Administration has fired an official who frequently was entertained by a Washington-area company while it was gaining a virtual monopoly as a result of FDA decisions.

Mary Bruch, a microbiologist, was wined and dined from New York to San Francisco and repeatedly entertained at several race tracks between 1974 and 1979. During that period, Burton, Parsons & Co. of Seat Pleasant, the company that entertained Bruch, gained control of the manufacture and marketing of the only cleansing and purifying solutions for soft contact lenses that the FDA permitted to be sold.

In 1974 the firm, which is owned by the locally prominent Manfuso family, had annual sales of only about $5 million. But by 1979, John A. (Tommy) Manfuso Jr. -- who ran the company along with his brother Robert and their father -- sold Burton, Parsons to Alcon Laboratories of Fort Worth, a subsidiary of Nestle' S.A. of Switzerland, for $110 million, according to industry estimates.

Another FDA employe who was entertained by Burton, Parsons, Dr. Arnauld Scafidi, resigned last spring after the House subcommittee on oversight and investigation conducted hearings on the affair.

Bruch was informed on Aug. 28 by the assistant secretary of Health, Dr. Edward N. Brandt Jr., who had reviewed her case, that she faced termination. The grounds for her firing were that she accepted meals, entertainment and gifts over a long period from a regulated company, according to a spokesman.

Bruch has 20 days from Friday, her official termination date, to request a hearing before the Merit Systems Protection Board. Bruch's attorney, Steven Engelberg, refused comment about whether his client will challenge the decision.