The United States has launched a major diplomatic effort aimed at containing the fighting in Lebanon, averting an Israeli war with Syria, and minimizing Soviet involvement.
But US diplomacy seems to be lagging behind swift-moving events. Israel clearly holds the initiative in Lebanon. Indeed, before full American pressure can be brought to bear on Israel, the Israelis may have achieved most of their military objectives in Lebanon.
The US obviously has enormous leverage over Israel in the form of economic aid and weapons supplies. But President Reagan has chosen, for the time being at least, not to threaten to cut off that aid. Short of this, the Americans appear to be powerless to influence Israeli moves.
Complicating the picture on the American side is the fact that some conservative elements in the Reagan administration favor the objectives that Israel is pursuing in Lebanon -- as long as the fighting does not go beyond that country. Official US statements on the subject have shown considerable sympathy for the Israeli objective of removing the threat of Palestinian artillery to northern Israel.
But some State and Defense Department officials who have their doubts about the virtues of the Israeli invasion predict privately that it will tend, at least temporarily, to push the Palestinians as well as Arab governments in what the US would consider to be more radical positions.
''I can't imagine that any moderate Arab government would step forward and help with the Palestinian question in ways that we would like after this,'' said one State Department official.
The official said that as far as the projected resumption of Egyptian-Israeli negotiations over ''Palestinian autonomy'' are concerned, ''things look pretty dismal.''
Those officials who would favor a more open condemnation of Israel and the use of heavy use of American leverage to secure an Israeli withdrawal from Lebanon are said to include Secretary of Defense Caspar W. Weinberger. Mr. Weinberger is reported to fear the impact that the invasion will have on Arab attitudes toward the United States.
But most US officials still seem to be betting that despite the wide sweep of Israeli military operations in Lebanon, Syria will avoid an all-out war with the Israelis. State Department officials say that the prime US objective at the moment is to help prevent the war from spreading to Syria.
Acting Secretary of State Walter J. Stoessel Jr. told reporters that American concern over the possibility of the invasion erupting into a wider Middle East conflict is one of the reasons why the US is calling for a cease-fire. Arguing that a cease-fire is its first priority, Mr. Stoessel declined to speculate on whether the US would impose sanctions on Israel.
Those in the administration who at least tacitly go along with Israel's invasion objectives seem to be counting on a restrained reaction from Arab nations outside Lebanon -- and from the Soviet Union. Other officials fear, however, that if the Israeli attackers crossed into Syria, the Soviet Union would then feel obliged to take action to maintain its credibility in the region. As it is, one official described the Soviet reaction thus far as ''remarkably restrained.''
The Arab reaction so far has been so restrained as to cause a Lebanese diplomat to refuse more than a minimal comment on it.
''I haven't seen an Arab reaction,'' he said.
White House officials, meanwhile, confirmed that President Reagan, as part of the US diplomatic effort, had sent an urgent message to Soviet President Brezhnev and to other leaders with influence on the parties to the conflict. White House counselor Edwin Meese III said that Reagan also sent Israeli Prime Minister Menachem Begin a ''very persuasive and friendly -- but firm'' letter calling for a cease-fire and Israeli troop withdrawal from Lebanon.
There was a time in the past when the US pulled out all the stops and threatened a full cutoff of American aid, thus halting a major Israeli military action. That was in 1956, when then President Dwight D. Eisenhower, by threatening an end to aid, got the Israelis to withdraw their invasion force from the Sinai.
The National Association of Arab Americans (NAAA) this week listed the obvious options for the Reagan administration: (1) a suspension of transfers of US economic and military aid pending an Israeli withdrawal from Lebanon; (2) a determination that Israel's use of American weapons in Lebanon violated the US arms export control act; (3) legislation aimed at freezing aid increases for Israel proposed for fiscal year 1983; and (4) cancellation of plans to sell Israel an additional 75 F-16 jet fighters valued at $2.7 billion.
It appeared unlikely, however, that the administration was even considering any of these options.