John Douglas Clark Sr., 74, a lawyer specializing in transportation matters who had practiced here since 1947, died Friday at Northern Virginia Doctors Hospital after a heart attack.

In recent years, he had been associated with the law firm of Garson, de-Member and Weiner in Fairfax.

Mr. Clark was born in Rice, Va. He graduated from Lynchburg College in Virginia and Franklin Law College in Columbus, Ohio. He was admitted to practice before the Ohio and Virginia bars, the Interstate Commerce Commission and the U.S. Supreme Court.

After working for 17 years as a telegrpaher, traffic rate clerk and in other jobs with the Norfolk and Western Railway, he became a traffic manager for the Youngstown, Ohio, Chamber of Commerce in 1943.

He came to Washington two years later as commerce counsel for the American Trucking Association. In 1946-47, he was assistant commerce counsel with the Chicago Association of Commerce and Industry before returning here to enter private practice of law.

Mr. Clark was a lay minister of Annandale United Methodist Church and a 32nd degree Mason. He lectured on transportation at Southeastern University in Washington and Pennsylvania State University.

He is survived by his wife, Mary Elizabeth, of the home in Annandale; two sons, John D. Jr., of McLean, and William S., of Annandale; a daughter, Eleanor M., of Annandale; a brother, Edward W., of Roanoke; three sisters, Ruby Abbott, of Covington, Va., Ruth Mays, of Amherst, Va., and Helen Roy, of Madison, Va., and three grandchildren.

The family suggests that expressions of sympathy may be in the form of contributions to the Heart Fund.