If the plan for the evacuation of the Palestine Liberation Organization (PLO) from west Beirut is carried through to a successful conclusion, the United States should be able to salvage a measure of credibility for itself in the Arab world.
This despite officially sponsored anti-US demonstrations in Kuwait and Damascus at the beginning of this week.
But the US is likely to get little respite.
Its credibility will almost immediately be put to the test on the question of autonomy and self-determination for the Palestinians. These are code words for a Palestinian state on the West Bank of the Jordan and in Gaza -- where 1.25 million Palestinians have been living under Israeli occupation since the third Arab-Israeli war of 1967.
Israel is resolutely opposed to any such state being inserted geographically between itself and the Kingdom of Jordan. The present Israeli government maintains that Jordan, within its current frontiers east of the Jordan River, is the natural homeland for the Palestinians.
The US government could therefore find itself in continuing collision with Israel, even if there is some resolution of the present crisis in Lebanon. That collision would be exacerbated if Israel's next steps -- to ensure that Jordan became the Palestinian homeland -- included pressures on Palestinians under Israeli occupation to leave for Jordan and measures to destabilize the hitherto relatively steady position of King Hussein of Jordan.
If and when the future of the West Bank and Gaza becomes the main issue between the US and Israel, the US has one important legal card to play. That is Israel's acceptance in ''the framework for peace in the Middle East'' signed at Camp David Sept. 17, 1978, of the concept of ''full autonomy'' for the inhabitants of those two Israeli-occupied territories.
One other likely development is that those 1.25 million Palestinians will become increasingly important as principals in the unfolding drama, if the PLO hard core to be evacuated from west Beirut is broken up and dispersed among three or four neighboring Arab countries.
There is no public suggestion that the PLO withdrawal from Lebanon should be immediately followed by the withdrawal of Israeli troops back to Israel. Conceivably the Israelis could link their own withdrawal to concessions by the US in their favor on the future of the West Bank and Gaza.
At the moment, neither Arab governments nor Arab public opinion give the US credit for what it has been trying to do through special envoy Philip C. Habib. That is, in effect, to rescue the PLO from the military trap in besieged west Beirut so that it can continue to fight for Palestinian rights -- at least in the political and diplomatic arena.
The Arab perception is that the US has been helping Israel more than the PLO. Most Arabs are convinced that the US, as Israel's patron, could force the latter to dance to its tune, if Washington really so wanted.
Arab governments in particular find the US a useful whipping boy because of their own failure to do anything effective to help the PLO since the Israelis launched their invasion of Lebanon more than nine weeks ago.
Ironically, the only Arab government willing to accept punishment from the Israelis at the Palestinians' side has been that of Syria -- and then only in a limited way. Yet in the general Arab line-up, Syrian President Assad has been odd-man-out, spoiling last year's Saudi peace proposals for the Middle East and siding with non-Arab Iran in the Gulf war between the latter and Arab Iraq.
But the Palestinians have no illusions about Syria's commitment to them. They know that if President Assad has to choose between them and his perception of Syrian interests, he will turn his back on them -- as he did in 1976 when he sided militarily with Lebanon's Maronite Christians to prevent the PLO from becoming the most dominant force in that troubled land.
The Palestinians know, too, that whatever PLO units move to Syria from west Beirut will be kept on a very tight leash by Mr. Assad. If there is to be any eventual unpleasantness with Israel, he will insist on having his finger on the trigger so that no Palestinian calls the shots.
The same goes for the other Arab governments offering haven for the PLO men to be withdrawn from Lebanon. Their national interests are going to come first. They are more aware than ever after the events of the past 10 weeks of Israel's military might and willingness to use it ruthlessly. And none of them is likely, without second thoughts, to risk inviting down upon itself that kind of Israeli clobbering.