Jean McCardell Williams, 71, a former teacher and fashion consultant long active in social service groups, died of cancer Sunday at her Clarke County, Va., home.

Mrs. Williams was born in Falls Church. She was a direct descendant of Revoluntionary War Capt. Peter Humrickhouse of the Philadelphia Regiment, who was a special aide to Gen. George Washington.

Educated at Western High School, the old Wilson Teachers College in Washington, and at the University of Maryland, Mrs. Williams was active in the area's Social Service organization.

In the 1930s, she headed the curriculum and textbook committees of the D.C. school system and was a demonstration teacher at Brightwood School.

She also served as a wedding consultant for the old Tailored Woman shop on New York's Fifth Avenue.

After her 1941 marriage to the Very Rev. Dr. J.L.B. Williams, Mrs. Williams became active in church social work. She helped establish Episcopal parishes in Millwood, Va., and among Indians in Muskogee, Okla.

She was also active in church work in Alexandria, Bonn, Germany; Palm Beach, Fla.; Nice, France; Rome, London and Geneva.

While in France, she founded the Woman's Club of the Riviera, and in 1970, Princess Grace of Monaco presented her with a medallion honoring her hospitality work with American Servicemen in the Sixth Fleet and with tourists and international students there.

In addition to her husband, Mrs. Williams is survived by a son, Ian R.D., of Westmoreland County, Va.; a daughter, television actress Judith Barcroft (Mrs. Wisner Washam), of New York City; a half-sister, Mrs. Donald W. Nesbit, of Greensboro, N.C., and two grandchildren.