A. Leftwich Sinclair Jr., 74, a retired president of Haley's Inc., an automotive firm in Washington, died of cancer Feb. 28 at Winchester Memorial Hospital in Winchester, Va.

Mr. Sinclair graduated from Washington public schools and joined the old Haley Auto Body Co. in 1925. He remained with the firm, later called Haley's Inc., until his retirement in 1963, having served as its president for more than 30 years. He moved to Moorefield, W. Va., following his retirement.

Mr. Sinclair served two teams as president of the Washington Automotive Trade Association. He was a director of the National Automobile Dealers Association from 1954 to 1961.

He also was a member of the Metropolitan Washington Board of Trade, the Touchdown Club, the Capitol Hill Club, the Automotive Oldtimers, the Cosmopolitan Club, and the Columbia Historical Society.

Survivors include his wife, Elizabeth., of the home in Moorefield; three children, A. Leftwich 111, of Baltimore, and Edwin H. and Martha V., both of Cumberland, Md; a sister, Barbara Harrison, of Tuscaloosa, Ala., and three grandchildren.

The family suggests that the expression of sympathy be in the form of contributions to the American Cancer Society or to the Moorefield Volunteer Fire Department.