Robert Bacon Reese, 79, an economist who worked for the Agriculture Department for 38 years before retiring in 1990 as chief of its food consumption research branch, died June 10 at his home in Potomac. He had emphysema.

Mr. Reese came to Washington and joined the Agriculture Department in 1952. Over the years, he became an authority in the field of food preservation, including the use of nuclear irradiation. He also worked on studies on domestic food distribution and consumption and the efficacy of the pilot food stamp program.

He was a frequent department spokesman before congressional groups and was the author of more than 50 technical papers.

He was a member of the Washington Assembly and the Cosmos, Sherwood Forest, and Kenwood Golf and Country clubs.

Mr. Reese, who was born in Whittier, Calif., was a 1940 economics graduate of Whittier College and received a master's degree in agricultural economics from the University of California at Berkeley. Before coming to Washington, he managed his family's fruit ranch in Whittier.

During World War II, he served with the Navy in the Pacific and attained the rank of lieutenant commander. He retired from the Navy reserve in 1963.

His wife, the former Constance Fryer, whom he married in 1951, died in 1990. Survivors include four sons, Robert Townsend Reese of Alexandria, Everett French Reese of Sherwood Forest, Md., and Loren Fitzhugh Reese and Navy Cmdr. Thomas Langhorne Reese, both of Potomac; a sister; and six grandchildren.