Mollye Swanson Ridgley, 58, a resident of Washington for 38 years who had been active in community affairs, died of cancer Monday at Howard University Hospital.

She was born in Danville, Va., and came here as a teen-ager to earn a degree from Howard University. She remained here until her death except for two years in the late 1940s, when she and her husband, Dr. Garrett V. Ridgley, a dentist, lived in Boston.

Mrs. Ridgley was a past president of The Bakers' Dozen Youth Center and of the LaSalle Elementary School PTA here. She had served on the PTA's Citywide Committee for Exceptional Children.

She had participated in the Attorney General's Committee on School Dropouts. She was active on the Building Committee of All Souls Unitarian Church and in the NAACP.

In addition to her husband, she is survived by a son, Dr. Garret V. Jr., and a daughter, Monifa Murry, all of Washington; three sisters, Anne Drew of Washington, Catherine Barlow of Hartford, Conn., and Marguerite Hopkins of Danville; five brothers, Carroll and Gregory Swanson of Washington, Frederick Swanson of Columbus, Ohio and Harry and Julian Swanson of Danville, and three grandchildren.

The family suggests that expressions of sympathy be in the form of contributions to the Special Cancer Research Fund in care of Dr. LaSalle D. Leffall Jr., at Howard University Hospital.