The Palestine Liberation Organization without Yasser Arafat is as unthinkable as 19th-century Italy without Garibaldi.

A partial explanation for Arafat's durability lies perhaps in the collective Palestinian pysche of the underdog unwilling to change leaders in a hostile world.

It also seems likely that the new middle-class educated Palestinian elite simply has kept its distance, preferring a loose arrangement akin to political and emotional consultancy for the PLO leadership, rather than permanent links.

Such hesitation is understandable in the light of th revulsion of many Palestinians against the guerrillas' excesses -- whether racketeering or high living among the remaining fleshpots that post-civil war Beirut still affords. l

Even more chilling was the rumored punishment meted out to Ibrahim Sus last summer. A highly articulate and talented concert pianist chosen as PLO mission chief in France -- largely to counter the Palestinian asterrorist image -- Sus was called back to Beirut for overstepping policy guidelines.

Accused of initiating contact with Israeli dissidents, the story goes, Sus was hauled before Abu Iyad, a senior Arafat aide, and soundly worked over by thugs.

For an organization known for its legendary reluctance to discipline major offenders guilty of theft, rape or other serious crimes, the messages of the Sus eposide came through loud and clear: PLO policies are determined in Beirut.

PLO insiders do not hide the manifold failings of the organization although, when challenged, PLO officials tend to fall back on routine replies -- "Remember, we're members of the Third world" or "The Israelis are like the Crusaders, and they only lasted 100 years."

Nevertheless, the insiders are aware that second best is not good enough when faced with the dedication, skill and intelligence that have distinquished Zionism since its turn-of-the-century beginnings. Indeed, they make no secret of their desire to emulate Zionist methods.

Walid Khalidi, a patrician Palestinian who teaches at both Harvard and the American University of Beirut, has suggested that the PLO is in organizational terms where the Zionists were in the 1920s -- "still outsiders waiting to change the status quo."

His own suggestions are for the PLO to adopt a more structured decision-making process, canvass more widely, seek outside advice and systematized its intelligence gathering before asking the political leadership to make up its mind.

Despite the PLO's checkered record, none of the younger, educated elite has challenged the 50-year-old Arafat and his middle-aged fellow leaders.

Suspicion of the motivated and encapable has been part of the PLO heritage since the late 1960s when an influx of enthusiastic and talented Palestinians infused a sense of purpose that has not been educated since.

Many volunteers from this period either were killed in the Jordan fighting or dropped out, disgusted by PLO disorganization, mediocrity, highhandedness and seeming inability or unwillingness to reform itself.

Similar was the experience of some 1,200 university students rushed back from overseas to Lebanon in 1976 to defend the PLO against the Syrian Army invasion. They fought well took heavy casualities, but after the fighting tended to drift away. Ironically, many of these "best and brightest" are no longer the children of the old elites. Many have been brought up from childhood by Fatah organizations such as the Cub Scout-like Ashbel organization and later sent abroad for higher education on Fatah scholarships.

The PLO leadership is also suspicious of the old elites. "They have made us feel unimportant," an upperclass and highly motivated Palestinian woman said. "We're occasionally useful as bankers, or couriers, but never really trusted despite our knowledge of the outside world and how it works, something they desperately need."

PLO appologists insist that the quality of its cadres is improving as Arafat and his colleagues realize that brains are essential to prepare a future state and that real effort must be expended to improve the PLO image in the United States.

At present, payrolls are met on time, extensive welfare and school projects function normally and PLO diplomacy passes muster. But political organization, public relations and military operations leave such to be desired by the Palestinians' own reckoning.

Even security is porous, perhaps because of their fondness for overlapping, rival intelligence-gathering organizations. Various PLO representatives abroad have been assassinated over the years either by the Israelis or hostile Arab governments.

Last winter, Abu Hassan, Arafat's personal security chief, was blown up in West Beirut by a remote-controlled explosive device. His error was neglecting the elementary precaution of changing itineraries and residences often enough.

A few months later Zuhair Mohsen, nominal chief of PLO military operations and Syria's top man inside the commando structure, was gunned down in the French Riviera resort of Cannes. He was indulging his love of gambling, scarcely the image Palestians like to cultivate either for home or foreign consumption.

Abu Iyad admitted as much in an interview in which he said: "We have become bourgeois. Each [leader] held out for his own ear, his own bodyguards. . . We were impressed by parades and applause."

But, the real danger is the PLO's seemingly incorrigible habbit of allienating the few Arab societies in which Palestinians are allowed to move about freely. Few lessons were learned from the commandos' debacle in Jordan in 1970 and 1971 -- or even from the near fatal involvement in the Lebanese fighting five years later.

"They destroyed one state to make their own," is the kind of remark once limited to right-wing Lebanese Christians determined to rid their country of the some 400,000 Palestians. Now, that kind of bitterness is shared by almost all of Lebanon's mosaic of communities.

The Palestinians are in the process of alienating the Shiite Moslems of southern Lebanon who, on paper at least, should be their natural allies against the devastation unleashed upon them both by the Israelis and their Christian surrogates along the border.

In the final analysis it is the threat of major military thrusts, either with outright Israeli participation or perhaps only covert backing, which constitutes the great threat to Arafat's continued leadership.

Yet, the PLO seems powerless to end its excesses in the south where its military presence, boxed in between the Syrian and United Nations forces, is at best a symbol justifying its more meaningful diplomatic operations.

"We're in a very dangerous situation for a liberation movement," said Palestinian journalist Imad Shakkour, "because we're caught between contradictory influences and desires."

Yes, the 1973 war proved that the Israelis were not invincible. Yes, the Arabs finally did use their oil weapon -- and could do so again for Palestine. Yes, the pro-Israel shah was over-thrown by pro-Palestinian Iranian revolutionaries. But, Egypt hs concluded a separate peace thereby all but dooming hope of any military solution.

"We are not used to winning," Shakkour said. "We know how to lose, how to deal with losing.

"For hundreds of years, since the Islamic conquest waned, we were used to equating war with loss. Taking the initiative implies treachery, mediation implies conspiracy in our minds.

"Contact with foreigners has meant the Arabs -- and especially the Palestinians -- being taken for a ride. Now winning means having to discuss victory, having to do something about it."

Doing something about it in the past, even some of the PLO's harshest critics claim, would have been to no avail. The Arab regimes weren't ready to stop playing with the PLO: the world's oil dependence was not yet critical; the oil weapon was unthinkable.

Yet, grave doubts persist about the PLO in its present form. "They've wasted too much of their substance in inter-Arab quarrels," a normally sympathetic analyst remarked recently. "In the meantime, the Israelis keep making more settlements in the West Bank.

"So far at least, the present Palestinian leadership has failed as badly as the earlier generation. The Israelis succeed in keeping marginally ahead, not quantitiatively, but qualitatively.