Robert Edward Day, 70, a retired administrator with the Department of the Interior, died Thursday at Fairfax Hospital. He had suffered from a rare metabolic disease for several years.

Mr. Day joined Interior in 1946 as assistant to the secretary. He later worked there in defense mobilization.

He joined Interior's office of the assistant secretary for energy and materials at the time of the oil embargo crisis in 1973. He retired in 1975.

From 1931 to 1933, Mr. Day worked for the market research department of W. J. Kellogg, in Battle Creek, Mich. While there he helped found the Battle Creek chapter of the Junior Chamber of Commerce.

From 1933 until the outbreak of World War II, he was director of placement at Northwestern University.

Mr. Day came to Washington in 1942 as the War Production Board's principal liaison officer with the Senate. In 1944, he was named special assistant to the chairman.

He was born and reared in Chicago. In 1929, he graduated from Northwestern University, where he majored in economics.

During the 1940s and 1950s, Mr. Day worked actively to improve the schools in Arlington County.

He was a member of the Arlington Parent-Teachers Association and the Arlington Symphony Association. He also was an American Red Cross and Community Chest fund-raiser for many years.

Survivors include his wife, Ruth, of the home in Alexandria; two sons, Robert Edward Jr., also of Alexandria, and Loren Allen, of New York City; a daughter, Catherine Joan, of Boston; two sisters, Dorothy Butler, of Alexandria, and Mary Harrison, of Washington, and four grandchildren.

The family suggests that expressions of sympathy may be in the form of contributions to the Fairfax Hospital Association.