Hildegard Wilson Cannan, 73, a scientist at the National Institutes of Health for nearly 20 years who was active in civic and environmental organizations, died Monday at Washington Hospital Center of complications following surgery for a hernia.

Dr. Cannan was a research endocrinologist at the National Cancer Institute from 1952 until she retired in 1971.

She had served as secretary of the Committee for 100 for the Federal City, editor and secretary of the Potomac Valley Conservation and Recreation Council, and board member of the Rachel Carson Trust fro the Living Environment. She had belonged to the North Cleveland Park Citizens Association.

She was the widow of Dr. R. Keith Cannan, chairman of the medical sciences division of the National Academy of Sciences from 1953 to 1967. He died in 1971.

A native of Bridgehampton, N.Y. Dr. Cannan earned a bachelor's degree at Cornell University of Illinois, and doctorate at New York University.

Before moveing to this area she had worked at the Sloan Kettering Institute for Cancer Research in New York, and was a biochemist in a number of New England laboratories.

She is survived by a stepdaughter, Dr. Cecily C. Selby, of New York City: a brother, Simon Wilson, of Chevy Chase; and three sisters. Herta Cavenaugh, of Baltimore, Mary H. Wilson, of Washington, and Mildred Noce, of Sperryville, Va.

The family suggests that expressions of sympathy be in the form of contributions to the Rachel Carson Trust or the Washington Humane Society.