Mary A. Hepburn, 70, president of the Montgomery County Council in 1965 and a member from 1962 to 1966, died of cardiopulmonary failure Tuesday at her home in Mesa, Ariz.

In addition to serving on the County Board, Mrs. Hepburn had been active in Republican state organizations. Before winning election to the Council, she had been president of the Montgomery County Federation of Republican Women, and then of the Maryland State Federation, and vice chairman of the Republican State Central Committee.

A lawyer, Mrs. Hepburn also had been chairman of the County Board of Zoning Appeals and legal counsel for the National Federation of Republican Women.

During her years on the county Council, she became known as a friend of the county police and a foe of juvenile delinquents. She favored a broader tax base for the county and sought to bring business to the county. She also favored county legislation to combat the proliferation of highway billboards.

Mrs. Hepburn left the County Council to run for the Maryland House of Delegates in 1966, but dropped out of the House race to devote more time to assisting the successful gubernatorial drive that year of Spiro T. Agnew.

She and her husband, William A. Hepburn, moved from Rockville to Frederick County later that year. About 1970, they moved to the Virgin Islands where they lived until moving to Mesa in September 1979.

Mrs. Hepburn was a native of Washington and moved to Rockville in 1948. She attended George Washington University and earned a law degree at Catholic University's law school.

She maintained a private law practice in Washington and Virginia for more than 20 years, and had served for a time as a government attorney with the Library of Congress, the Reconstruction Finance Corporation and the War Department.

Mrs. Hepburn was a member of the American, District, and Virginia bar associations.

In addition to her husband, of Mesa, her survivors include a sister, Frances O. Freund of Dale City, Va.