Syria's expulsion of Yasser Arafat today left the chairman of the Palestine Liberation Organization, for the first time in the guerrilla movement's history, without a perch, much less a base, in a front-line Arab state facing Israel.

For various, often contradictory reasons, Egypt, Jordan, Syria and with it Syrian-controlled Lebanon are effectively carrying out Israel's long-term goal of depriving the PLO of any pretense of a military role, which in turn conferred meaningful independent political clout.

Unless and until Syria relents--and in the past reconciliations between Arafat and President Hafez Assad have taken a long time--Arafat seems condemned to what one diplomat called the fate of "an unguided missile flying in ever smaller circles" far from the Middle East action.

In some ways, Arafat today looks more washed up than at any time since he founded Fatah in 1965--if Syria has dropped its long war of attrition against his authority in favor of a quick kill. But Arafat is the Arab world's quintessential survivor.

His critics--many of whom have been emboldened by the seven-week-old mutiny against his authority inside the mainstream Fatah organization--consistently warned that Arafat had no choice but to accept effective Syrian control of the PLO.

Such, they argued, was the unavoidable consequence of the PLO's losing its state-within-a-state status when it was forced to evacuate Beirut last year as a result of Israel's invasion of Lebanon.

Until April 22, that was a political reality Arafat was not ready to accept. On that day he agreed to meet Assad in a formal act of obeisance following the breakdown of his talks with King Hussein of Jordan, one of Syria's arch enemies.

Within weeks the mutiny erupted, with Arafat followers whispering that the Syrians were behind it but publicly accusing only Libya.

Then on Tuesday Arafat made the fateful decision to accuse Syria openly of aiding and abetting the rebels.

How much Syria actively backed the rebels is difficult to ascertain. But since the loss of Beirut, all Palestinians--loyalists and dissidents--have been condemned by geography and their lack of access to independent ports to depend totally on Syria.

Arafat's decision to set up his post-Beirut headquarters in faraway Tunis was deeply regretted by Syria and questioned by many Palestinians who argued that Damascus was the only possible choice because of the traditional Syrian role in providing the PLO's strategic depth.

Arafat was motivated by tactics and emotion. As long as the moderate Arabs encouraged his eventually abortive efforts to reach an agreed stand with Hussein on negotiations over the future of the Israeli-occupied West Bank and Gaza Strip, Arafat could hardly be on good terms with Syria, which vehemently opposed that U.S.-backed initiative.

The Reagan administration's open hostility to a PLO role in such negotiations--and its unwillingness to prove its credibility by persuading the Israelis to leave Lebanon during the winter--further alienated Syria and many Palestinians accused Arafat of selling out. Fresh in their minds was the failure of U.S. pledges to protect the lives of hundreds of Palestinians in the Shatila refugee camp in Beirut last September.

Emotionally, Arafat and those who fought alongside him in Beirut were in no mood to accept the domination of Syria, which they judged to have left them in the lurch and deprived them ever since of arms and ammunition.

But the long absence of Arafat and his principal lieutenants from Syria and Syrian-controlled Lebanon where his fighters were stationed seriously eroded his political power base.

Ill-considered promotions and nominations of officers perceived by the rank and file to be corrupt or to have fled the battlefield sparked the long-smoldering rebellion.

Some Palestinians contended Arafat still failed to understand how deep-rooted these complaints are and instead prefers to place all blame on Syria and Libya.

His time-honored tactic of appealing to friends in the Arab and non-Arab world has brought sympathy from allies as ideologically different as Saudi Arabia and the Kremlin. But neither the rebels nor the Syrians have been moved.

Now that he has been expelled, Arafat will almost certainly gain support not only from friendly governments but also from nearly all Palestinians living in the occupied territories or in the diaspora.

Yet the prize in this conflict is not those Palestinians, but rather the 12,000 to 15,000 fighters now stationed in Lebanon.

"Those men's families for the most part live in Syria," a rebel adviser said, "and obviously they are anxious about their fate."

He claimed that the mutiny was proceeding without a hitch although he, too, expressed surprise at the expulsion.

All along the rebels staked their strategy on wearing Arafat down slowly, winning over enough of his troops to accept formal negotiations eventually on something approaching an equal footing.

It remains unclear whether Syria's decision--and the inescapable implications of wanting not just to cut Arafat down to size but effectively eliminate him--will change the rebels' thinking. But there was an unmistakable weight of logic behind the adviser's conclusion.

"We are not conducting a coup," he said. "Once Arafat is off our backs, we will start rebuilding the military organization to attack the Israelis. And if we--and not Arafat--do that, where is his claim to leadership?"

However convincing that argument may sound, the fact remains that for many in the outside world--and the overwhelming majority of Palestinians--Arafat is "Mr. Palestine" and the personal embodiment of the PLO.

The rebels may well win--and Syria with them--only to find out they have lost the very thing Arafat personally built and then mistakenly thought could save him: his international stature.