Dr. William D'Aguanno, 56, an assistant associate director for new drug evaluation at the Food and Drug Administration, died of cancer Monday at Georgetown University Hospital.

Dr. D'Aguanno joined the FDA in 1956 as a pharmacologist and worked on problems relating to public health. In 1964, he was assigned to the review of investigative and new drug applications and specialized in toxicology.

In 1966, he was named supervisory pharmacologist in the division of neuropharmacological drugs and in 1968 was promoted to deputy director of that division. In 1970, he was named chief pharmacologist in the FDA's bureau of drugs. From 1974 until his death, he was assistant associate director for new drug evaluation, a position in which he dealt with all aspects of pharmacology and toxicology in the bureau of drugs.

Dr. D'Aguanno was born in Providence, R.I. He was a hospital corpsman in the Navy during World War II and then returned to Rhode Island, where he took a degree in zoology at the University of Rhode Island. He earned a degree in physiology at the University of Oklahoma and a doctorate in physiology at Florida State University in 1955.

He moved to the Washington area and began his career with the FDA in the following year.

Dr. D'Aguanno's survivors include his wife, the former Beatrice Pirolli of Rockville, where the family lives; three daughters, Marie, Jane Ann and Donna Louise, all of Rockville, and a sister, Irene Marsella, and two brothers, David and Roland, all of Rhode Island.

The family suggests that expressions of sympathy be in the form of contributions to the Rockville Presbyterian Church, 215 West Montgomery Ave., Rockville, or to a charity of one's choice.