If plans are eventually agreed for the United States Sixth Fleet and Marines to evacuate the Palestinians trapped by the Israelis in west Beirut, it will be one of the most decisive American interventions in the Middle East since the Marines went ashore in Lebanon nearly a quarter of a century ago.
President Reagan's decision to use US forces to promote a Lebanese settlement would then take its place with other rare acts of American resolution in the interest of peace at critical moments in the Arab-Israel conflict.
* President Eisenhower's no-nonsense pressure on Israel, Britain, and France to secure their withdrawal from Egyptian territory after the 1956 Arab-Israel war.
* Former Secretary of State Henry Kissinger's diplomacy to force a cease-fire on Israel at the end of the 1973 Arab-Israel war in order to keep open the door for the negotiations which eventually led to an Egyptian-Israeli peace treaty.
* President Carter's personal intervention and commitment in 1978 to ensure conclusion of that treaty by way of the Camp David accords.
In the efforts to resolve the current Lebanese crisis, it was the Lebanese government itself which took the first step by asking the United States about the feasibility of a plan involving American troops.
The reaction of the other parties most directly involved, the Israelis and the Palestinians, offers a typically Middle Eastern paradox. The Palestinians appear to be rejecting the plan and the Israelis to be accepting it - even though its implications seem to favor the Palestinians rather than the Israelis.
Certainly, Palestine Liberation Organization leader Yasser Arafat's reaction sounds like rejection. But his form of words leaves room for eventual acceptance.
Mr. Arafat told the New York Times: ''We are not in need of American help. The weapons and the Sixth Fleet that helped kill my women and children cannot protect us. Definitely I won't accept it.''
But he added that he was ''in favor of an international effort for disengagement'' of Palestinian and Israeli forces in the Beirut area. French military involvement alongside the US Marines - which is part of the tentative evacuation plan - could be interpreted as making the operation international and not just American.
Mr. Arafat and President Assad of Syria are choosing to represent the proposed US intervention to rescue the PLO as continued collusion of the US with Israel to ensure destruction of the PLO and the imposition of an Israeli-style peace on the whole Arab world.
Yet the implications of the US initiative are in many ways favorable to the PLO.
If the US provides safe-conduct for up to 6,000 PLO and other Palestinian activists out of west Beirut, that would come very close to American recognition of the PLO which the latter has long demanded.
And implicit in US action to preserve a Palestinian political identity - in the face of a threatened Israeli military onslaught on west Beirut - there is a US intention to proceed eventually to a broader Middle East settlement which would address the question of Palestinian self-determination, as promised in the Camp David accords.
This would mean eventual US pressure on Israel to enter into more meaningful negotiations about the future of the West Bank and Gaza where 1.25 million Palestinians have been living under Israeli occupation since 1967.
In some ways, then, it is surprising that - on the surface at least - it is the Israelis who are responding positively to the plan and the Palestinians who are rejecting it.
At the same time, one should not overlook the proven negotiating skills of Israeli Prime Minister Menachem Begin which in the past have turned seemingly initial concessions into stepping-stones for the implementation of maximalist hard-line, long-term Israeli strategy.
That it should be Ronald Reagan willing to send in Marines in effect to keep a Palestinian entity alive is all the more remarkable in that he was perceived as being the most pro-Israeli president to enter the White House since establishment of the state of Israel.
The circumstances under which US Marines went ashore in Lebanon in July 1958 were very different from those of today and were not directly connected with the Arab-Israel conflict. In 1958 then President Chamoun of Lebanon asked for US intervention to prevent what he (and President Eisenhower) saw as a Soviet-backed move to bring the whole of the Arab Middle East under then Egyptian President Nasser's pan-Arabism.
A contingent of British troops responded to a parallel call from King Hussein of Jordan.
Neither the US nor British troops were subsequently involved in any fighting, and they were withdrawn three months later.