I think that one of the most influential foreign policy events of 1979 that influenced the direction of America's diplomatic and military endeavors had to be the Iran Hostage Crisis. The crisis of United States hostages at the American Embassy in Tehran proved to be a watershed moment in modern American foreign policy. President Carter could not rescue the hostages and negotiations with the captors failed miserably. Carter was perceived to be terribly ineffective, at best, and at worst, dangerously incapable of dealing with a new world order. The event helped to bring Carter's presidency to a screeching halt and assisted in convincing the American public that Ronald Reagan had the answers. With Reagan's ascendancy into political office, American foreign policy became defined in a more "exceptionalist" manner, ensuring that American strength and almost domination would be present in each and every aspect of its foreign policy. The Iran Hostage Crisis became a rallying point in which Reagan and America itself felt that should never happen again. With this in mind, US foreign policy became more assertive and was guided with this "exceptionalist" view of America at the center of the nation's diplomatic and military approaches to foreign policy.
The most important event in 1979 having to do with US foreign policy was the Iranian revolution and hostage crisis. This event has continued to impact US foreign policy down to the present.
When Iranians rebelled against the Shah, the US became their major enemy because it had supported the Shah and his repressive regime. Since then, Iran has been ruled by a theocracy that is very anti-US and is, since Ahmedinejad has been in office, also very openly anti-Israel. The hostility of Iran towards the US has a huge impact on our foreign policy. Right now, one of the biggest worries the US has in the Middle East is the problem of Iran's nuclear program and its more general interest in undermining US interests around the region.
Because it continues to have an impact today, the Iranian Revolution was the most important event in 1979 when it comes to US foreign policy.