Alex R. Rodriguez, formerly medical director for the Defense Department's civilian health benefits program for military families, has announced he will leave his post to become vice president and medical director of Preferred Health Care Corp., a New York-based firm that operates one of the largest national health benefits programs.

Donald J. Donahue, chief executive officer at KMI Continental, has been elected chairman of the board of its affiliate company, Life Insurance Co. of Virginia. Both companies are subsidiaries of Continental Group Inc. In addition, R. Bern Crowl, chief financial officer of Reynolds Metals Co.; William B. Harman Jr., a partner in the law firm of Sutherland, Asbill & Brennan; Raymond F. Henze III, senior vice president for Pacific Holdings Inc.; and Donald L. Sturm, senior vice president of Peter Kiewit & Sons Inc., have been elected members of the board.

Early, Cassidy & Schilling Inc., an independent insurance agency in Bethesda, has announced the promotion of Frederick H. Merther to president and Robert J. Kelly to executive vice president. Merther succeeds Gerald K. Cassidy, who will continue as chairman and senior officer of the firm. Kelly, a director of the Bethesda-Chevy Chase Chamber of Commerce, replaces Walter Schilling, who will remain as vice chairman and treasuer.