Gustavus Tuckerman, 78, a retired Foreign Service officer, died of a heart attack Wednesday at his summer home in Westpoint, Maine.

His last assignment before retiring in 1969 was that of an instructor at the Foreign Service Institute here. He moved from Washington to Hanover, N.H., five years ago.

An economist and authority on Russia and Eastern Europe, Mr. Tuckerman had joined the Foreign Service in 1948. In 1950, he was assigned to London for three years. In the late 1950s, he played a key role in handling the Soviet Trade Show in New York and its American equivalent in Moscow.

Born in St. Louis, Mo., Mr. Tuckerman attended the University of Wisconsin. He was a graduate of the University of Missouri and the London School of Economics.

He taught economics at New York University from 1929 to 1941, when he entered federal service here.

Mr. Tuckerman was with the War Production Board, the Department of Agriculture and the United Nations Relief and Rehabilitation Administration before joining the State Department.

He is survived by his wife, Ethel Kate Zachow Tuckerman, of the homes, and two sisters, Cornelia Stadler, of Ann Arbor, Mich., and Mrs. William Carter, of Phoenix, Ariz.