Mabel Louise Robinson, 76, a longtime Washington resident who was a retired officer of the American Institute of Cooperation, died Sunday in a hospital in Hollywood, Fla., after a stroke.

She worked for the institute for about 25 years before retiring as its assistant secretary and treasurer in 1970. The institute is an educational organization that works with farm cooperative organizations.

She taught business and secretarial courses at the old Woods College in Washington during the early 1940s before beginning her career at the institute.

Mrs. Robinson was a native of Washington and a resident of Montgomery County before moving to Hollywood three years ago. While living in Maryland, she had been active in the Republican Party and the Monocacy Homemakers Club of Montgomery County.

Her first husband, Claude Murphy, died in 1934. Her second husband, W. L. Robinson, a retired traffic safety director of the American Automobile Association, died in January 1980.

Mrs. Robinson's survivors include a daughter by her first marriage, Doris Willard of Alexandria; two sons by her second marriage, William L. Robinson Jr. of Greenbelt, and John W. Robinson of Rockville; a brother, James S. Raleigh of Hollywood, Fla., and nine grandchildren.

The family suggests that expressions of sympathy be in the form of contributions to St. Mary's Catholic Church, Box 67, Barnesville, Md.