Mordecai H. Gordon, 66, a retired administrator of research grants at the National Institutes of Health, died Tuesday at Holy Cross Hospital in Silver Spring. He had a heart ailment.

Dr. Gordon, a clinical psychologist, joined NIH in 1959 as a staff adviser in the National institute of Neurological Diseases and Blindness. Two years later, he became executive secretary of the mental health study section in the research grants review branch. He held this and simialr posts in the U.S. Public Health Service and the National Cancer Institute until his retirement in 1976.

Much of Dr. Gordon's work in the various branches of NIH was with grants review boards. Those are panels of outside experts who make recommendations on the allocation of research funds, based on the priority of the proposed projects and their apparent chances of success.

Dr. Gordon was born in Tarrytown, N.Y. He was educated at New York University, Columbia University and the University of Tennessee, where he earned a doctorate in clinical psychology in 1950.

After World War II service in the Army, he became a clinical psychologist at the Veterans Administration Hospital in Memphis, Tenn., and continued to work toward his doctorate. He later worked at VA hospitals in Ohio, Iowa and Maryland, where he was assistant director of the VA Central Neuropsychiatric Research Laboratory at Perry Point from 1957 to 1959.

Dr. Gordon was a fellow of the American Psychological Association, a fellow of the Maryland and D.C. psychological associations, a member of the American Statistical Association, and numerous other professional organizations, He published articles in several technical journals.

Survivors include his wife, Edna, of the home in Kensington; a daughter, Joan Gordon of Iowa City, Iowa; a sister, Leah Bernstein of Huntington Woods, Mich., and two brothers, David, of Larchmont, N.Y., and Harry H., of Mamaroneck, N.Y. CAPTION: Picture, DR. MORDECAI H. GORDON