Margaret Cushman Fleming, 77, who was active in civic, hospital and charity work in this area, died Friday at her summer house in Port Republic, Md., after a heart attack.

Mrs. Fleming, who lived in Washington, was born in Ithica, N.Y. In 1923, she married John R. Fleming, a writer and journalist. She and her husband came to this area in 1930, when Mr. Fleming began working for the government.

A speechwriter for former vice president Henry A. Wallace when Mr. Wallace was secretary of Agriculture, Mr. Fleming later was chief of publications for the Office of War Information. He retired in 1970 as world report editor for the U.S. News and World Report.

Mrs. Fleming was a volunteer with the Rosemary Hills Elementary School PTA in Silver Spring. She also was a fund-raiser and volunteer for Suburban Hospital in Bethesda, and was active in the League of Women Voters and the Montgomery County Thrift Shop in Bethesda.

Besides her husband, of the homes in Washington and Port Republic, survivors include three sons, John R. Jr., of Buffalo, N.Y., Philip A., of Washington, and Thomas C., of Bethesda; a brother, Blinn S. Cushman of East Hampton, L.I., N.Y., and five grandchildren.