Margaret Lillian Downing Thornton, 89, a Washington resident for 44 years who was active in church groups, died of a coronary thrombosis Friday at the Wisconsin Avenue Nursing Home.

Mrs. Thornton, who had lived at the Wisconsin Avenue home for several years, was an active members of the Henson Valley Christian Church in Oxon Hill, formerly the Ninth Street Christian Church of Washington. She was a longtime Sunday school teacher there and a member of Church Women United.

She and her husband, Rowland Gipson Thornton, moved here from Schenectady, N.Y., in 1936, when Mr. Thornton went to work for the Naval Weapons Plant here. He died in 1964.

Mrs. Thornton was born in Northampton County, Va., and graduated from the Powhatan Institute in Virginia. From about 1914 to 1924, she was a dental technician in Richmond.

Survivors include a daughter, Margaret T. Whiteman of Scotia, N.Y.; a sister, Pearl D. Bull of Newport News, Va., five grandchildren and eight great-grandchildren. A son, Army Air Corps Lt. Rowland G. Thornton Jr., was killed in World War II. Another son, William S. Thornton, died in 1975.

The family suggests expressions of sympathy be in the form of contributions in her name to the Henson Valley Christian Church in Oxon Hill.