Margarette Brooks Rydell, 56, a Washington area resident for 40 years who was active in the Alliance Francaise and in women's church and PTA groups, died of cancer Sunday at her home in Silver Spring.

As a longtime student of French and a member of the Alliance Francaise, Mrs. Rydell for a number of years conducted tours of Washington in French and English for visitors.

Mrs. Rydell was born in New Bern, N.C., and reared in Bucks County, Pa. A pianist, she moved to Alexandria with her family as a girl and studied at the Washington School of Music. During World War II, she worked at the Pentagon for the Army Signal Corps.

She was a member of the altar guild at the Episcopal Church of Our Saviour in Silver Spring. She was active in the Hillandale Women's Club, having served as club president, secretary and editor of its newsletter, and had served on the boards of several Silver Spring Parent-Teacher groups.

Survivors include her husband of 37 years, Paul E., a son, John, and a daughter, Robin Black, all of Silver Spring; another daughter Nancy Richardson of Walnut Creek, Calif.; her mother, ann Brooks Paschal of Vienna; a sister, Pat Davis of McLean, and a granddaughter.

The family suggests that expressions of sympathy be in the form of contributions to the American Cancer Society.