Aug. 20, 1953//Prime Minister Ousted in Coup//The Central Intelligence Agency backs a plan, coordinated with British intelligence, to overthrow the Iranian prime minister, Mohammed Mossadegh. The plan has the approval of President Dwight D. Eisenhower and is conceived because of British concerns over petroleum exports and the relationship of the prime minister with the Soviets. The coup, orchestrated by an American agent, leads to the ouster of Mr. Mossadegh, and the shah, Mohammed Reza Pahlavi, becomes an authoritarian monarch.