Beirut — The Palestine Liberation Organization has surprised everyone - except perhaps itself - by holding out so long, remaining united, and even now inflicting significant damage on the Israeli invaders of Lebanon.
Despite that, however, the PLO's political stock seems to have fallen drastically.
Its welcome, even by sympathetic Lebanese, has worn thin. The PLO's Arab allies continue to put up what an American diplomat calls ''a thunderous silence'' in the face of Israeli efforts to destroy it. And they refuse to give it refuge except on their own strict terms.
The PLO's often-fractious leaders, realizing that the choice before them today is between independence and a last-ditch stand, agree that staying and fighting may be best. The very existence of the PLO may therefore be at stake here.
The Lebanese and most other Arabs see the PLO at this point more as the poor loser, dragging innocent Lebanese down with it, than as the plucky survivor.
Yasser Arafat's recent rhetorical comment, ''Did Churchill leave London during the blitz?'' was quietly criticized by several prominent, otherwise sympathetic Lebanese, as presumptuous. They pointed out to the Monitor that Beirut is the Lebanese, not the Palestinian, capital.
Similarly, when George Habbash of the Popular Front for the Liberation of Palestine suggested making Beirut the PLO's ''Stalingrad'' - or, more recently, its ''Hanoi'' - a number of Lebanese discreetly criticized Mr. Habash for abusing the PLO's guest status here.
This seems to run counter to previous (and, admittedly, less drastic) Israeli assaults on the PLO. During heavy Israeli raids last summer, the PLO suffered serious military setbacks. It took most of last fall and winter to recover from them. But it seemed to benefit from the underdog image and from the negative publicity Israel received for using its fighter-bombers against the Palestinian-Lebanese Fakhani neighborhood in Beirut where the PLO has made its headquarters.
This time, however, the PLO's early military losses were made up for by the strength of its last redoubt: the city of Beirut. Six weeks after the vaunted Israeli Army entered Lebanon and five weeks after it sealed off Beirut, Israel is quite reluctant to go in after the PLO. In fact, Israel is having to adjust to the PLO's residual military muscle.
Perhaps the PLO's most impressive military feat came July 11. For weeks Israeli armor and artillery had been bashing Palestinian positions in west Beirut with only mild response from the PLO's showy but inaccurate Katyusha field rockets. Soldiers staffing Israeli supply depots and rear line camps had been basking in the breezy, pastoral hills outside Beirut.
But on July 11, the Palestinians surprised the Israelis with cannons, mortars , and rockets. They hit these Israeli positions, destroying a number of vehicles , and causing, according to Israeli Col. Paul Kader, 31 Israeli casualties in one day. Three of them were fatal.
The Israelis responded with an intense day-long bombardment of west Beirut before another truce was worked out late July 11. Colonel Kader estimated 10,000 shells were fired. As a result of the Palestinian attack, Israeli headquarters and supply depots were being relocated July 12.
''I was surprised by Palestinian fire power,'' the colonel, Israeli's official military spokesman, admitted.
Besides its Beirut arsenal, the PLO seems to have on its side both time and an unquantifiable horror element in the possibility of a pitched battle for Beirut - a battle Israel would have to initiate.
The prolonged negotiations that are being conducted to avert a final Israeli-PLO showdown in Beirut have been slogging along for five weeks. As time passes, Israel not only loses military momentum but pressures at home and abroad mount on Israel.
Colonel Kader admitted July 12 that ''it appears time may be working in their (the PLO's) favor. . . . Every day creates a new dynamic in the negotiating process which appears to serve their purposes.''
Indicative of this new dynamic, the colonel felt, were:
1. The American plan to send United States forces to supervise a PLO evacuation.
2. Syria's recent refusal to give refuge to the hardcore PLO guerrillas.
3. The Soviet Union's reactions to the American plan and its expressions of continued support for Syria.
To these must be added current reports from Washington that the Reagan administration has threatened Israel that the US may begin direct negotiations with the PLO if Israel is not more forthcoming in diplomatic negotiations led by US envoy Philip C. Habib.
''There is no intention of the Israeli government allowing itself to be dragged into a war of attrition or an open-ended negotiating process,'' Colonel Kader said.
But there seemed little choice at this point.
In some ways the miring down of Israel outside Beirut was a function of the unpopularity of the PLO in the Arab world. No Arab country has come forward to give unconditional refuge to the PLO. Several have attached conditions on the number of Palestinians they will accept or on the scope of these Palestinians' future political activities. Among these are Egypt, Algeria, Iraq, and Syria (which, ultimately, and with a cash incentive from Saudi Arabia, might be willing to harbor a subservient PLO).
Nor have Arab countries gotten together to take the measures they have within reach. There has been no oil weapon, no severing of relations with the US, and no emergency Arab summit conference. This is because the PLO may be as much an annoyance to the conservative Arab regimes (even the pro-Soviet ones) as it is to Israel.
Still, the Arab world makes a point of reiterating its view that the PLO is the sole legitimate voice for the Palestinian cause. But since the Camp David era began in 1978 there has, in fact, been a functional distinction between the PLO in Lebanon (radical and distant) and the Palestinians of the West Bank and Gaza (immediately repressed and users of little more than civil disobedience).
What influence the PLO has had on Palestinians under occupation, Israel is attempting to eliminate by giving the PLO the choice of evacuating and losing independence or staying and being physically crushed. No matter the length of time the PLO can hole up in Beirut, either way it seems to face the end of its political life.