経済協力局
In 1946, Averell Harriman, then Secretary of Commerce, picked Foster to be Under Secretary of Commerce, in part to help with rebuilding Europe after the war. When President Harry Truman launched the Marshall Plan for that purpose in 1948, Harriman became the Special Representative of the effort in Europe and Foster became his deputy. Foster was Administrator of the Marshall Plan (formally the Economic Cooperation Administration) for 1950–1951.