Daniel S. Masterson Jr., 50, a research chemist with the Food and Drug Administration since 1959 and a president emeritus of the Washington Forensic League, died Nov. 27 at Suburban Hospital after a heart attack. He lived in Bethesda.

Mr. Masterson was a native of Washington and graduate of Gonzaga College High School. He earned bachelor's and master's degrees in chemistry at Georgetown University before joining the FDA's old antibiotics division. For the past year, he had worked in its division of bio-pharmaceutics.

From 1959 to 1969, he was a debate coach at Ursuline Academy in Bethesda, then coached a year at Georgetown Prep. At the time of his death, he was a debate coach at both St. John's College High School and Immaculata High School.

He was president of the Washington Forensic League for more than 10 years before becoming president emeritus in 1979. He had been a host for the finals of the national speech and debate contests, and was the recipient of a citation for service from the Churchillian Classic.

Mr. Masterson was a member of the St. Jane de Chantal Catholic Church in Bethesda.

Survivors include his mother, Louise Masterson, and a sister, Louise Valenti, both of Bethesda, and a brother, the Rev. Thomas D. Masterson, S.J., of Scranton, Pa.