Theodore L. Sweet, 79, who retired from the Agency for International Development in 1970 after 30 years of government service, died at the Kent County Hospital in Warwick, R.i., Dec. 27 following a series of strokes.

Mr. Sweet was born in Providence, R.I. He graduated from Brown University there and earned a degree at the Harvard business school. He was the New England sales manager of the Rumford Chemical Works until 1941, when he moved to Washington to begin his government career.

He was an official of the old War Production Board and was an economist attached to the military government in Germany after the war. He joined the Economic Cooperation Adminstration, which administered the Marshal Plan, and remained with that and other foreign assistance agencies until AID was formed in 1961. Mr. Sweet was a branch chief in the field of technological assistance at the time of his retirement.

Mr. Sweet continued to live in Sumner, Md., until 1977, when he retired Warwick, where he had maintained another home for many years. He was a member of the Montgomery Players in Gaithersburg, a member of St. David's Episcopal Church in Washington, and a 32d degree Mason.

Survivors include his wife, the former Mary Emerson, of Warwick, two sons, William L. II, of Bethesda, and James Y., of Bad Aidling, Germany; a daughter, Sandra Y. King of Boise, Idaho, and 12 grandchildren.