Keith R. Potter was elected to fill a vacant seat on the board of Preston Trucking Co. of Easton, Md. He is vice chairman of International Harvester Co. and a graduate of Baltimore Law School.

Russell C. Clark of Kensington has been appointed to the position of vice president-control at Pace Associates, a consulting firm specializing in postal matters that recently opened a District office. The president is Charles L. Pace, who resigned after 10 years as director of postal relations with Newsweek Inc.

Robert B. Stewart has been named to the newly created position of manager, product and planning, by James River Corp., the largest independent U.S. producer of specialty papers.

Ronald P. George has been named director of sales of Aztech Corp., a Washington-based computer service firm.

Frank J. Quirk has been elected president and chief executive officer of Macro Systems Inc., a D.C.-based management consulting, applied research and computer systems firm. He joined the firm in 1972 as vice president after working for the management consulting firm of Booz, Allen & Hamilton Inc.

Don P. Kredel has joined the accounting firm of M. B. Hariton and Co. as director of management advisory services.

Ralph L. Shifley was elected vice chairman of the Stanwick Corp. of Arlington. He has served as president and treasurer since August 1978. Tad Stanwick, chairman of the board, has reassumed the position of president and Gordon E. Hamlet was elected treasurer.

Larry L. Marsden has been appointed product marketing manager of manufacturing systems for STSC Inc., a Bethesda-based computing services and software products firm. Terry L. Enos has joined the company as manager of manufacturing systems.

Kristin M. Smith has been named director of business development of Interspace Inc./Washington, a unit of Interspace Inc., a national interior design and space planning firm.