Elbert G. Mathews, 66, of former ambassador to Nigeria and Liberia and a career minister, died Monday at Sibley Memorial Hospital after a long illness.

Mr. Mathews served as ambassador to Nigeria from 1964 to 1969, when Nigeria was racked by civil war. The province of Biafra was attempting to secede.

At one point, Ambassador Mathews expressed the "deep concern" of the United States for the civilian population of Biafra. This concern centered on reports of famine there and the bombing of civilian facilities in the secessionist state.

Following his service in Nigeria, Mr. Mathews coordinated the senior seminar in foreign policy at the Foreign Service Institute until he retired in 1972.

He began his foreign service career in 1935, and held a number of positions in five countries on three continents during the next 10 years. He then held assignments in the State Department in Washington.

From 1959 to 1962, he was ambassador to Liberia, and attained the rank of career minister.

In 1963, Mr. Mathews was named director of the Office of Inter-African Affairs, a post he held until leaving for Nigeria as ambassador in 1964.

Born in Troy, N.Y., he earned a bachelor's degree from the University of California at Berkeley.

Mr. Mathews was a member of the Washington Institute of Foreign Affairs, the American Foreign Policy Service Association, the International Club and the City Tavern Club.

He is survived by his wife, Naomi M., of the home in Washington.