Dr. Francis S. Ronalds, 87, a retired historian with the National Park Service and a founder of the National Trust for Historic Preservation, died of congestive heart failure Feb. 18 at the Carriage Hill Nursing Home in Silver Spring. He lived in Washington.

Dr. Ronalds was born in Grayville, Ill. He graduated from the University of Illinois, where he also earned his doctorate in history. He later received a law degree from Indiana University.

He moved to Washington in 1936 as chief historian of the National Park Service. In 1939, he was transferred to Morristown, N.J., to take charge of national parks and historic sites in New England and the mid-Atlantic states.

In this post, he was instrumental in making many of the agency's major acquisitions, including Franklin D. Roosevelt's home in Hyde Park, N.Y., the Vanderbilt mansion, which also is in Hyde Park, and the Adams mansion in Quincy, Mass. In addition to his regional responsibilities, he was the superintendent of the Morristown National Historical Park at the time he retired in 1967.

His wife, Grace M. Ronalds, died in 1980 and he returned to Washington.

Survivors include a son, Francis S. Jr., of Washington; five grandchildren and nine great-grand children.