The once proud and powerful administrative headquarters of the Palestine Liberation Organization's capital-in-exile is a gutted and forlorn symbol today of the military defeat that was inflicted on the guerrillas and on the entire Arab world last summer.

Stripped down to its window frames by the Israeli Army that occupied West Beirut in September after the PLO's leaders and fighters evacuated the city, the old headquarters on Corniche Mazraa has traded the PLO emblem that used to hang from its second-floor balcony for a lighted picture of Bashir Gemayel -- the slain Christian militia chieftain who had advocated expulsion from Lebanon of the half million Palestinians who have gathered here since the founding of Israel.

Lebanese Army security men interrogate any Lebanese or Palestinians who come to the door of this building, from which for a decade the PLO's kaffiyeh-clad soldiers with their AK47 assault rifles emerged to hop into jeeps and roar about a city descending into anarchy as dozens of local and foreign-supported militias battled each other.

All that ended in August, after what the PLO calls "The 74-Day War" with Israel. Having fought longer against the Israelis than had the armies of Egypt, Syria and Jordan in the 1956, 1967 and 1973 Arab-Israeli wars, the guerrillas accepted U.S. mediation and sailed out of Beirut to end the campaign that Israel said would wipe out the PLO as a political and military force and open the way for true peace in the Middle East.

It was the second time in little more than a decade that PLO leader Yasser Arafat had seen his forces shattered militarily and had been forced to flee a revolutionary headquarters. In September 1970, I and other correspondents watched King Hussein's Jordanian troops crush the PLO guerrillas in Amman. Arafat survived only by being smuggled out to Cairo in disguise.

Israel has been quick to emphasize the similarities of Amman 1970 and Beirut 1982. But in their new exile, PLO leaders emphasize the differences, and say why the differences show that the PLO remains a major force in the Middle East four months after the last PLO fighter sailed out of Beirut.

From Amman, the PLO troops left unheralded, in ridicule. From Beirut, they left in a compromise negotiated by the United States, waving their Kalashnikov rifles. Arafat left not in the middle of the night but with an emotional dockside sendoff from the Lebanese prime minister, a French Navy escort and U.S. air cover.

Still struggling to shape a strategy to deal with its new situation, the PLO today is shaken but stubbornly unbowed. Its mood is glum but, oddly, not desperate. There is a grim realization that the struggle that has molded their lives is doomed to continue far into the future.

"As we say in Arabic, ours are tough bones, not easy to crack," Arafat said in a recent interview at his new headquarters in a rambling seaside hotel at Bourj Cedria, Tunisia, about 1,500 miles from the homeland the PLO seeks for its scattered followers.

At 52, with his scraggly beard starting to whiten, Arafat has few illusions left about the difficulties of his struggle. He has been defeated before, yet survived. He remains confident that he will survive again.

"They talk of the Chinese Long March of Mao Tse-tung," Arafat said. "This is our Long March, and it is already more than 6,000 miles long."

There is a tinge of fatalism in this view that undermines hopes in the world that Beirut will prove a catalyst to force the PLO leaders to compromise their basic demands that the Palestinians be given the right of self-determination and an independent state in at least a corner of the land they once occupied.

Arafat seems to know how badly the odds are stacked against him. He is well aware that virtually every strategy he has tried in the past has failed.

Hopes that the consciences of his fellow Arabs would unite them behind the PLO to confront Israel were not borne out. Expectations that an alliance with the Soviet Union would produce results also were dashed this summer when Moscow displayed total impotence to affect events in the Middle East.

And the expectation in the ranks of the PLO that its diplomatic efforts to get Washington -- and, through Washington, Israel -- to accept it as the only possible representative of the Palestinians in any future peace negotiations appears to be fading rapidly.

But for Arafat there is the knowledge that for each past failure of strategy, each defeat of his forces on the ground, his movement has somehow grown in stature -- among the Palestinian people it seeks to unite and among the nations of the world it hopes to influence.

An extended search through the Palestinian diaspora for the meaning of the summer's war in Lebanon yields evidence of such pluses and minuses for the PLO. It is possible to see at least as many signs of the durability of the basic elements of the Middle East crisis as of the changes wrought this summer.

Talks with Palestinian leaders, academics, businessmen, elected officials and destitute refugees, from Tunisia to Syria to the Israeli-occupied West Bank, indicate that though the Beirut summer has moved the crisis into a new, yet uncharted phase, the fundamental forces that created it have not been significantly altered.

The conclusions that one can draw at this point are:

*Although defeated on the ground by Israel this summer, the PLO has emerged with its leadership and organizational structures basically intact, with Arafat's authority and freedom of political action enhanced, the Palestinians' sense of national identity heightened and the PLO's claim to represent them stronger than ever before.

*The PLO's military pretensions, always more illusory than real, have been shattered for a long time to come -- though, because the image of armed struggle is so deeply rooted in the mythology of the PLO, the organization will continue to talk of its "military options" and not renounce the possibility that it will wage war with Israel again.

*The vast state within a state that the PLO built in Lebanon as a model of the institutions and structures it hoped someday to implant in Palestine has been destroyed, and the half million Palestinians it served have been left in a worse state of insecurity than at any time since the PLO came into being.

*In the Israeli-occupied West Bank and Gaza, where the mushrooming spread of Jewish settlements already is threatening to preclude any possibility of the land being turned back to Arabs in any form, the mood in favor of seeking compromises with the Israelis has been offset by a renewed sense of loyalty to the PLO, to which the final decision on negotiations has been entrusted.

"Arafat is fond of saying that the Palestinians are the odd number in the Middle East equation," said one West European ambassador in Damascus. "Nothing that has happened this summer has changed that. Anyone who thinks the PLO has now been eliminated as a key factor in any Middle East peace does not understand the Middle East problem."

Defeat at the hands of the Israelis this summer, after a resistance of 74 days, has apparently reinforced the moral dimension of the PLO's struggle in the eyes of the Arabs and even much of the rest of the world.

"Amman was a complete tragedy because it ended up in a war between Arabs, Palestinians and Jordanians," Arafat admitted in a recent interview in his Tunisian headquarters, recalling the period now enshrined in Palestinian mythology under the name of Black September. "Beirut was something different: We were not fighting brother Arabs, but the Israeli enemy. We were defending an Arab capital, defending Arab honor, standing up before the world for the whole Arab nation."

In many ways, the battle of Beirut was an inevitable next step after the battle of Amman, where the PLO had rooted itself after the 1967 Arab-Israeli war. There, suddenly, the PLO found itself challenging an Arab ruler, King Hussein, for control of his capital and, ultimately, his kingdom. The radicals within the PLO proclaimed that Amman had to be seized before Jerusalem could be regained, that conservative Arab governments had to be overturned before the Palestinian revolution could triumph.

When the king finally turned on the PLO after a wave of airliner hijackings had landed three commercial jets laden with innocent hostages in his desert, he defeated the PLO in his capital in a violent, no-holds-barred civil war. The idea that a "military option" existed for the PLO against the Arab governments suffered a devastating defeat.

Arafat's troops were left behind by their chief to fight their last futile battles under the command of Khalil Wazir, known under the nom de guerre of Abu Jihad, before being forced out of the city and into the barren Ajloun Hills to the north, where they were allowed to camp through a cold, bitter winter before being attacked once more and expelled from Jordan to seek a new capital in Beirut.

Although Arafat and his regrouped PLO eventually went on to make many of the same errors of arrogance in Lebanon that they had made in Jordan, they struggled hard to avoid direct confrontation with the Lebanese government and concentrated on a stunning buildup of artillery and conventional armor along the southern border with Israel.

That buildup helped trigger the Israeli invasion, even though the PLO had kept its guns along the border quiet for nearly a year in a U.S.-arranged truce. That truce underscored the central fact that whatever clout the PLO has managed to establish in the Middle East during the years -- and that clout has often been overestimated -- did not depend on those strutting armed men in the streets who became its symbol to the world. It depended on the force with which Arafat would wield the moral issue of the Palestinian cause, especially with his proud fellow Arabs whose repeated humiliations by Israel since its founding in 1948 he used as his political capital.

"Arafat's only real strength has always been his fellow Arabs' sense of guilt and shame about their failure to prevent Israel from taking over an Arab land," an Arab ambassador in Tunisia said. "His power comes from the ability he has shown to manipulate the very Arab rulers that are seeking to manipulate him and his movement, by playing on the guilt that challenges their own sense of legitimacy."

In the view of many Palestinians, it is one of the sources of their national tragedy that their struggle has been not only against the Israelis, whom they accuse of illegally and violently usurping the land of their ancestors, but also against their fellow Arabs, whom they have alternately had to shame or manipulate for their support.

Everywhere the Palestinians have gone in the Arab world they have been treated as pariahs, forced to stay in refugee camps, denied equal rights, passports or even a sense of identity. It is such indignities at the hands of their fellow Arabs--indignities that continue to this day and which are as much the cause of the PLO's arming itself as the struggle against Israel--that fueled the Palestinians' determination that only with their own state will their human rights be guaranteed, their leaders now acknowledge.

"There is not a man of my generation who doesn't bear the scars from his youth of the whips of various Arab intelligence services," said the 44-year-old Abu Jihad in his Damascus apartment, after recounting how he had been hounded by Egyptian intelligence agents in Gaza, where he grew up, and, later, by the Jordanians, who banned him from their kingdom for 20 years.

"We Palestinians have always been treated as strangers by other Arabs, considered traitors just because of our insistence on being Palestinian," said Abu Jihad, today the equivalent of the PLO's minister of defense. "We picked up guns because we had suffered so much, both from Israel and our own Arabs."

It is that struggle against the Arabs who have variously wanted to control or repress them in the 34 years they have been fighting from exile that lies at the heart of Arafat's own struggle to establish the PLO's political independence. Paradoxically, the Israeli invasion of Lebanon appears to have strengthened Arafat's ability to resist Arab governments who want to use the PLO as an instrument of their own national politics.

In the midst of so many defeats, Arafat and the men immediately around him have established themselves solidly as representative of Palestinian interests, even if minor splinter groups among the eight separate organizations that make up the PLO still respond to the politics of nations that finance them, such as Syria, Iraq and Libya.

With his own leadership strengthened this summer by his having stood by his troops to the end, Arafat is seeking, so far with apparent success, to move the PLO to adopt the sort of moderate, conciliatory stance that might erase its past image of intransigence and thus encourage Washington to consider it a valid participant in any future peace process.

While Arafat and many other of the most important PLO leaders privately express a real desire to find a negotiated settlement, they insist that such an accommodation can come only if their demands for an independent homeland are met.

If they are not, the men of the PLO insist, the struggle that has taken them from Jerusalem to Amman, to Beirut, and now to such distant homes as Tunis and Aden, will somehow go on and on. If they cannot pry loose the homeland they insist is their right, then they are determined to keep the Middle East in turmoil.

"We have been through many disasters, and yet we have survived," says Khaled Fahoum, the Damascus-based chairman of the Palestine National Council, the PLO's parliament-in-exile. "The Jews survived for a long time too. Don't you think we can? We want peace, we want a settlement, but we want a settlement that is just and that recognizes our basic right. Until we get that, there will be instability in the Middle East. We will not give up until we have a homeland like everyone else."

Next: Fighters chafing in exile