Paul L. Day, 80, retired health science administrator with the National Health, Lung and Blood Institute, died of cancer Friday at Suburban Hospital in Bethesda.

He joined the National Institutes of Health in 1962 and retired in 1973. He lived in Bethesda.

Dr. Day was born in Grants Pass, Ore. He graduated from Williamette University in Salem, Ore., and earned a master's degree and doctorate from Columbia University.

A former teacher at Columbia Junior College in Milton, Ore., and Montana Wesleyan College in Helena, he joined the faculty of the University of Arkansas School of Medicine in Little Rock in 1927.

During his 31 years there, Dr. Day was a professor and head of the biochemistry department. He also was assistant dean of the graduate school during 1956-58 and conducted research that led to the recognition of folic acid as an important member of the B-vitamin complex involved in blood cell formation. He participated in research on nutritionally induced cataracts and the physiological role of vitamin E.

Dr. Day came to Washington in 1959 as the first scientific director of the Food and Drug Administration, and remaining there until joining NIH.

He was a charter member and former president of the Amercian Institute of Nutrition. He helped organize and was the first chairman of the central Arkansas section of the American Chemical Society. He belonged to the American Society of Biological Chemists.

Dr. Day has served on the editorial boards of the Journal of Nutrition, the Proceedings of the Society for Experimental Biology and Medicine and the Proceedings of the Animal Care Panel.

He had been a member of the food and nutrition board of the National Research Council, a member of the scientific advisory committee of the Nutrition Foundation and a member of the committee on animal nutrition of the agricultural board of the National Research Council.

He had received numberous awards from organizations in his field.

He is survived by his wife, the former Mildred Garrett of Bethesda; two daughters, Peggy Leppmann of Guelph, Ont., and Dr. Dorothy Ciarlo of Denver; a brother, Lester, of San Francisco, and five grandchildren.

The family suggests that expressions of sympathy be in the form of contributions to the Patient Emergency Fund of the NIH Clinical Center, Bethesda.