Helene Bryant Westerfield, 58, who was a special assistant to former D.C. mayor Walter Washington for seven years, died Monday at Columbia Presbyterian Hospital in New York City where she was being treated for cancer.

In addition to assisting the mayor with diplomatic and community relations, Mrs. Westerfield had been a special consultant to the State Department and was the mayor's liaison to the State Department's Protocol Office.

She was the widow of Samuel Z. Westerfield Jr., a former College dean and Treasury Department official who was ambassador to Liberia at the time of his death in 1972.

Mrs. Westerfield was a member of the board of directors of the International Student House and the Christ Child Settlement House. She also was a member of the Friends of the Museum of African Art and had served on the executive committee of the Desert Ball, a benefit given for countries of the Sahel south of the Sahara.

Mrs. Westerfield was a native of Birmingham, Ala., and attended Spellman College in Atlanta, where she was elected to Phi Beta Kappa and graduated summa cum laude. She earned a master's degree in social work at Simmons College in Boston.

She was a professor of social work at Atlanta University for eight years before moving to Washington and joining the faculty of Howard University in 1961.

Survivors include a daughter, Sheila, of the home in Washington; a son, Dr. Samuel Z. III, of St. Louis, and a brother, Dr. Henry Bryant of Ann Arbor, Mich.