Dr. Robert G. Rosenberg has been named executive director of Group Health Association Inc. in Washington. Since May 1982, he has been GHA medical director, a position he will maintain. Rosenberg was formerly medical director of the Rhode Island Group Health Association.

Charles B. Molster Jr., F. Curtis Barry and Phillip W. Mason have established a new data processing company, Molster, Barry & Mason Inc., in Richmond. The company will develop computer software for mail order houses and retailers selling through direct mail.

The three principals were formerly executives of Garfinckel, Brooks Brothers, Miller & Rhoads. Molster was corporate vice president for management information; Barry was manager of research and development, and Mason was manager of systems development of the GBM Corporate Data Center.

John Michael Zimmer has been named a principal and vice president of Delon Hampton & Associates, a Rockville engineering firm.

Daniel J. Harrold has joined the Washington law firm of Finnegan, Henderson, Farabow, Garrett and Dunner. Harrold had been a general attorney with Comsat since 1979.

Pierre Paul Childs, John J. Corley Jr. and Robert W. Nordstrom have been named vice presidents of the architecture firm of Harry Weese & Associates in Washington.

Peter D. Bergstrom has been promoted to head of the Mitre Corp.'s new communications and systems design department in McLean. He joined Mitre in 1973.

Harold F. Nelson II has been promoted to assistant manager and trader of the municipal bond department of Riviere Securities Corp. in Washington.

Lee B. Spencer Jr. has been named a partner of the Los Angeles-based law firm of Gibson, Dunn & Crutcher. Spencer was formerly director of the division of corporation finance of the Securities and Exchange Commission. He will work in the firm's Washington and New York offices.

Louis H. Nevins has been named a partner of the New York-based law firm of Thacher, Proffitt & Wood. Nevins will set up the firm's new Washington office. He was formerly senior vice president and director of the National Association of Mutual Savings Banks.

John M. Crawford has been appointed partner in charge of the Atlantic region of Deloitte Haskins & Sells. He was formerly partner in charge of the accounting firm's Washington office.

Pam Radford has established the Middleburg interior planning and design firm of Pam Radford Associates. Radford was formerly a principal of the firm of Radford Biddison.

David V. Lee has been named vice president of Chelsea Systems Inc., the McLean developer of microprocessor-based computer software and systems.

Nicholas Lutkins has joined Decisions and Designs Inc. of Mclean as an independent corporate design consultant.