Donald A. Melnick, 50, a consultant to operations research firms, died May 19 at his home in Silver Spring after a long illness.

He came here in 1954 to serve as senior physicist and project supervisor of Operations Research, Inc., in Silver Spring.

Later, Dr. Melnick was director of physical research at Raff Associates, Inc., in Silver Spring, director of the operations research and physical sciences department at CEIR, Inc., in Arlington, and president of Scientific Planning Associates Corp. in Silver Spring.

He had been a private consultant since 1971. He was the author of many publications covering antisubmarine warfare, antimissile engagement analysis, economics of depressed areas, flood control and election forecasting.

Born in Philadelphia, Dr. Melnick was a graduate of the University of Pennsylvania. After serving in the Navy in World War II, he received a master's degree from the University of California at Los Angeles and returned to the University of Pennsylvania to earn a doctorate in physics.

After coming here, he was active in the Montgomery County Republican Party and the Young Republicans. He was Republican precinct chairman in Takoma Park in 1960 and 1961, and served on the Montgomery County Civil Defense Advisory Commission in 1963 and 1964.

Dr. Melnick was a member of the American Physical Society, the Operations Research Society of America, the Institute of Management Sciences, the Washington Operations Research Council, the Federation of American Scientists, the Washington Association of Scientists and Phi Beta Kappa.

He is survived by his wife, Nannette, of the home; a brother, Dr. Joseph Melnick, of Philadelphia, and a sister, Vivienne Korman, of Georgia.