Washington-based Computer Network Corp. has named Philip Schatten, currently president of the firm's Com-Med division, to company vice president. In addition, Gary M. Siegel has been appointed president of its information systems division. Siegel, formerly president of the company's Com-Mail division, replaces Robert J. Werner, who has left the company to start his own business.

Tesdata Systems Corp. has appointed William S. McFadyen and Gerald B. Pinsky, vice presidents in charge of operations and marketing, respectively. McFadyen joins the McLean-based firm after ten years with GTE Communications Products. Pinsky was most recently director of marketing and sales for Infinet Inc.

Vycor Corp., a Washington-based computer sales and services firm specializing in facility management, has appointed Thomas E. Northam to its marketing staff. Northam has worked for the Facility Management Institute and as a consultant for Booz-Allen & Hamilton Inc.

Automatic Data Processing has named John Monahan accounting services manager for Anne Arundel and Howard counties. Before joining ADP, Monahan was an IBM dealer.

Pergamon Group has elected P. James Terragno president of Pergamon InfoLine Inc., a McLean-based electronic publishing and database company. Terragno had been an office director in the U. S. Patent and Trademark Office, before joining the four-year-old firm as executive vice president. Pergamon provides on-line access to summaries of patents, scientific articles and business directories.