Scope and Contents The Mutual Security Agency was established under the Mutual Security Act of 1951. It was set up to succeed the Economic Cooperation Administration December 30, 1957. W. Averill Harriman was appointed by President Harry S. Truman to serve as director to supervise the Mutual Security program. The same Advisory Board of Economic Cooperation Administration, with Hinckley still a member, continued to act in an advisory capacity to Harriman on policy matters relating to the Mutual Security program....