The Atomic Energy Act of 1946 that created the Atomic Energy Commission provided for a nine-man General Advisory Committee (GAC) to advise the commission on scientific and technical matters. Rabi was one of those appointed in December 1946. The GAC was enormously influential throughout the late 1940s, but in 1950 the GAC unanimously opposed the development of the hydrogen bomb. Rabi went further than most of the other members, and joined Fermi in opposing the hydrogen bomb on moral as well as technical grounds. However, President Harry S. Truman overrode the GAC's advice, and ordered development to proceed. Rabi later said:
Oppenheimer was not reappointed to the GAC when his term expired in 1952, and Rabi succeeded him as chairman, serving until 1956. Rabi later testified on Oppenheimers behalf at the Atomic Energy Commissions controversial security hearing in 1954 that led to Oppenheimer being stripped of his security clearance. Many witnesses supported Oppenheimer, but none more forcefully than Rabi:
Rabi was appointed a member of the Science Advisory Committee (SAC) of the Office of Defense Mobilization in 1952, serving as its chairman from 1956 to 1957. This coincided with the Sputnik crisis. President Dwight Eisenhower met with the SAC on October 15, 1957, to seek advice on possible US responses to the Soviet satellite success. Rabi, who knew Eisenhower from the latters time as president of Columbia, was the first to speak, and put forward a series of proposals, one of which was to strengthen the committee so it could provide the President with timely advice. This was done, and the SAC became the Presidents Science Advisory Committee a few weeks later. He also became Eisenhower's Science Advisor. In 1956 Rabi attended the Project Nobska anti-submarine warfare conference, where discussion ranged from oceanography to nuclear weapons. He served as the US Representative to the NATO Science Committee at the time that the term "software engineering" was coined. While serving in that capacity, he bemoaned the fact that many large software projects were delayed. This prompted discussions that led to the formation of a study group that organized the first conference on software engineering.