What policy toward communism did diplomat george f Keenan recommend?

He recommended "Containment", which remained the official US policy until after the Vietnam War. Its end was also influenced by the fact that it then also transpired that the 'Domino theory" of the USA was incorrect, which held that if one nation fell to Communism, all its neighbors were bound to follow. They didn't.

The Containment policy held that Communism should remain contained within the areas where it was dominant around 1949; and that any effort of Communist countries or forces to expand beyond those areas should be forcibly repulsed by the USA. This policy led to US involvement in Cuba (the Bay of Pigs-disaster and the missile crisis), in the Korean War and in the Vietnam war.