Robert B. Mang has been named president and chief operating officer of Woodward & Lothrop/John Wanamaker Inc., effective May 1.

Mr. Mang, 45, who will report to Arnold H. Aronson, the company's chairman and chief executive, is currently president of Bon Marche in Seattle, a division of Campeau Corp.

Woodward/Wanamaker includes 17 Woodward & Lothrop stores in the Baltimore-Washington area and 15 John Wanamaker stores in the Philadelphia area. The two chains are owned by Taubman Holdings Inc., a private investment concern controlled by A. Alfred Taubman, a leading mall developer.

Industry estimates say that the 32 stores had sales of about $900 million last year.