Allied Research Corp., a Baltimore-based defense contractor, bTC has named former Grumman official Jay R. Sculley president and chief operating officer.

Mr. Sculley takes over positions held by Reginald W. Carter, who was promoted to chairman of the board. Mr. Carter remains chief executive officer. The previous chairman, Marvin B. Ruffin, died Nov. 16, 1990. Both appointments were effective yesterday.

Allied, which once had manufacturing operations in the Baltimore area, has only five employees here now. Its main plant, with 391 employees, is near Brussels, Belgium, and produces ammunition and rifle grenades, said Richard Farrell, a company spokesman.

An engineering and design operation in Elk Grove Village, Ill., has 143 employees.

Mr. Sculley, a member of Allied's board, was the director of advanced studies and technologies for Grumman Corp., a major aerospace and defense contractor. He was assistant secretary of the Army for research, development and acquisition from 1981 to 1989.

Mr. Sculley is a graduate of Virginia Military Institute with a bachelor of science in engineering. He also holds master of science and Ph.D. degrees in engineering from the Johns Hopkins University.

Allied had record earnings last year of $14.2 million, or $3.38 a share, up from $23,000, or 1 cent a share, in 1990. The company attributed the improvement to increased automation, control of costs and concentration on products with short-term payoffs, such as ammunition.