Mary G. Thomas, 71, retired employe of the animal-plant health inspection service of the Department of Agriculture, died at Leland Memorial Hospital in Riverdale Saturday following a heart attack.

Mrs. Thomas was born in Pittsburgh. She moved to Washington in 1936 and went to work for the Treasury Department. In 1941 she married William V. Thomas, who also worked for Treasury. They were transferred to Chicago in 1942 and Mrs. Thomas continued to work for the department until 1944.

In 1948 the family returned to the Washington area. Mrs. Thomas went back to Treasury in 1958 and remained there for the next 10 years. In 1968 she moved to Agriculture, where she was a clerk in the health inspection service until her retirement in 1979.

Mrs. Thomas, who lived in University Park, had been a member of the parish of St. John de la Salle Catholic Church in Hyattsville at the time of her death. She also was a member of the Post Cara Club at St. John de la Salle and of several senior citizens groups in Prince George's County.

Her husband, who became a management analyst at Treasury, died in 1969.

Survivors include two daughters, Kathleen Welsh of University Park and Maureen E. Thomas of Washington; two sons, William V. Jr., of Washington, and Michael G., of College Park; a brother, John Nugent of Pittsburgh; Two sisters, Ellen and Catherline Nugent, also of Pittsburgh, and two grandchildren.