Ansgar Rosenborg, 85, a retired United Nations official, died of congestive heart failure Friday at his home in Bethesda.

Mr. Rosenborg joined the U.N. secretariat in 1946. He served as interim executive secretary of the Economic Commission for Asia and the Far East in 1947, and as a technical assistance official. He headed missions to Haiti in 1949 and Indonesia in 1950.

He was resident representative of the U.N. Technical Assistance Board in Indonesia in the mid-1950s, and later served as the personal representative of the secretary general in Guinea, before retiring in 1959.

Mr. Rosenborg was born in Gefle, Sweden, and was a graduate of Uppsala University. He joined the League of Nations secretariat in Geneva in 1921. He came to the United States in 1940 with the league's economic finance mission, which had headquarters at the Institute for Advanced Studies at Princeton University during the war.

Following his retirement from the United Nations, he lived for a time in Sweden before coming to Washington in 1974.

His wife, Sigrid, died in 1972.

Mr. Rosenborg is survived by a son, Tomas, of the home; two others sons, Staffan, of Washington, and Rutger, of Westfield, N.J., and seven grandchildren.