United States hopes that the siege of Yasser Arafat will nudge moderate Arabs into a workable peace process with Israel look at least premature. And the strengthening of a Syrian-backed rebel wing of Mr. Arafat's Fatah guerrilla group could complicate Washington's more immediate goal of achieving stability in Lebanon.
Much of the effect of the civil war in Arafat's Fatah guerrilla group, the largest in the Palestine Liberation Organization, will depend on if, how, and when he extricates himself from thunderous artillery duels with Syrian-backed rivals in the north Lebanese city of Tripoli.
Yet as the Tripoli fighting raged on, US Secretary of State George Shultz Saturday issued a new call for Jordan's King Hussein to join talks for peace with the Israelis.
Israeli officials, too, hope the Fatah fighting will so weaken Arafat - and so divide the PLO - that both King Hussein and local Palestinians in the Israeli-occupied West Bank and Gaza Strip will prove more conciliatory on the issue of peace negotiations.
Signals from rival Mideast parties suggest a muddier picture.
Two recent Fatah meetings - the latest in Tunis 11 days ago - suggest that if Arafat does leave Tripoli, he will seek to co-opt at least some of his rivals by taking a harder negotiating line.
A statement after the Tunis meeting seemed meant partly to counter speculation that a weakened Arafat would scurry to King Hussein to plot joint strategy with him and West Bank or Gaza Palestinians for peace talks.
The statement cited ''anticipated political dangers threatening the Palestinian struggle - whether the dangers come from the dissident clique or from the forces that are preparing to launch policies hostile to our people and their aspirations, particularly in Jordan and the occupied land.''
Moves by two main hard-line groups within the PLO to distance themselves from Syrian-backed Fatah rebels seem likely to encourage Arafat to reconstitute a viable, less concilatory PLO.
King Hussein is taking a wait-and-see attitude. In theory, he says, the ''door is open'' to new contacts with Arafat. Earlier this year, the two men seemed to be inching toward joint, conditioned acceptance of Reagan's plan for an eventual federation between Jordan and Palestinians in the West Bank and Gaza - though this would stop short of the PLO demand for a Palestinian state. Then Arafat balked. Hussein called off all bets.
But armed attacks on Jordanian diplomats abroad bombings in Amman could make the King think twice about taking a key role in any new peace initiative.
And if Hussein-Arafat contacts resume - or if the King decides to take a new look at the Reagan plan - Jordan will expect the US to make good on assurances it will get Israel to freeze West Bank settlement before any talks.
Israel seems in no mood for such concessions. Defense Minister Arens Saturday said he was confident the US wanted a strong Israel, and that this presupposed Israeli control of the West Bank.
Israel's stand is that any revived peace process must center on the original Camp David plan for limited Palestinian autonomy, minus Reagan's 1982 rider on eventual Palestinian federation with Jordan.
Israeli officials seem to feel things are moving their way. The Fatah civil war is seen as weakening PLO credibility as a negotiating party in any Mideast peace.
And the US needs Israeli cooperation in any removal of foreign forces - Israel's, Syria's, and, presumably, the US marine contingent - from Lebanon.
Sunday, Israel gave the latest signal of a more assertive military role since the recent attack on its headquarters in south Lebanon. Israeli jets bombed areas in the Syrian-controlled part of Lebanon. One jet is known to have been shot down. Syria claims two were hit.
Among Palestinians in the West Bank and Gaza, there is some sentiment that the longer the delay in a settlement, the less attractive the terms will be. There is even talk about reviving the Camp David autonomy plan as a basis for negotiation.
But there seems no support now for ''going it alone'' - without Arafat or, at a minimum, King Hussein. Partly, local Palestinians feel Israel is in no mood to cede even the ''full autonomy'' mentioned at Camp David. Partly, a West Bank figure says, there is concern that local figures who take the negotiating initiative could risk Syrian-supported reprisals.