When Palestine Liberation Organization Chairman Yasser Arafat addressed a gathering of Palestinian jurists here recently, he did his best to appear his old ebullient and combative self.

Arafat dismissed the 2 1/2-month-old revolt against his leadership, by dissidents of his Fatah organization in the Syrian-controlled Bekaa Valley of Lebanon, insisting that the Palestinian people as a whole had shown in statements and messages that they remain united behind him.

The issue, Arafat insisted, was not that of a split in Palestinian ranks so much as an attempt by Syrian President Hafez Assad, the rebels' most prominent backer, to gain control of the PLO.

But for all the chairman's rhetorical flourishes and and expressions of optimism about the ultimate outcome of the contest, the mood of his audience was glum and, among some, skeptical.

Although the jurists were loyal to Arafat, they were also distressed by the disarray in their nationalist movement since its forced expulsion from Beirut almost a year ago. No amount of upbeat talk by Arafat could change that.

"What is depressing is not just the black eye we are suffering because of a few rebels in the Bekaa," said a jurist who asked that his name not be used. "What bothers most is the realization that our leaders have proven powerless to do anything about it. Their strategy does not seem to be working and that is a sign they do not have as much power as we thought."

Arafat and his intimates in the scattered offices, resort hotels and seaside villas that make up the PLO's headquarters-in-exile here in the Tunisian capital are quick to dispute such a negative assessment. But they remain hard put to explain how they can overcome the challenge to the PLO leadership by Said Abu Musa and two dissident members of the Fatah central committee ao long as Syria supports them and continues to control the Lebanese arena of the rebels' challenge.

This failure to put forth a convincing strategy for dealing with the rebellion has placed Arafat on the defensive. He whirls among Arab capitals to plead for diplomatic help against the Syrians.

Although the mutiny has failed to gain momentum outside those areas directly under Syrian control, the fact that it continues is chafing Arafat.

"The fact is that everything the chairman has tried to do has so far failed to produce the desired results," one PLO official at the Hotel Salwa admitted in confidence. "The tragedy for us is that every dispute that remains unsettled is another day of lost credibility abroad and amongst our own people."

Mediation efforts--by the secretary general of the Arab League, the foreign ministers of Saudi Arabia, Algeria and Cuba, even a six-man delegation of the PLO's own executive committee--have gotten nowhere. The cease-fire effected by the PLO's delegation early last month collapsed two weeks ago into another round of almost daily armed clashes in the Bekaa.

PLO officials say Arafat gets promises of support wherever he goes--most recently from Saudi King Fahd--but they admit there is little evidence that the Arab nations' promised entreaties to Damascus have made any headway.

Hopes of enrolling the Soviet Union to use its influence on Assad also may have foundered. Encouraged by what the PLO has said were private diplomatic notes of support from Moscow, Arafat indicated privately in mid-July that he would soon be flying to Moscow to meet with Soviet Communist Party chief Yuri Andropov. But the trip was canceled, according to a PLO official, when the Soviets told an advance delegation that they would not openly interfere in a dispute be tween two allies even if they did not agree with Assad's anti-Arafat stance.

The Palestinian news agency WAFA said Tuesday that the visit is now to take place next month, Reuter reported.

To blunt the rebels' charges that his leadership was autocratic and undemocratic, Arafat last month reshuffled the structure of Fatah to give it an air of collective leadership. According to aides, he offered to sit down and talk to the rebels--within the democratic structure of the organization--about their criticisms.

Arafat also rescinded the appointments of two loyal but discredited military men to key commands in the Bekaa Valley. It was those appointments, of Abu Hajem and Haj Ismail last May to reinforce Arafat's influence in the Bekaa against pro-Syrian commanders, that sparked Abu Musa's revolt.

Because none of those efforts has borne fruit, Arafat has called on the PLO's 81-member Central Council to meet today on the split in Fatah and his dispute with Assad. The council is an intermediary body between his Executive Committee and the wider National Council, or exile parliament.

Arafat, according to aides, expects the council to give him a vote of confidence to show that among the Palestinians at large he is still the undisputed leader.

Officials close to the PLO leader say he feels that as long as Syria is determined to topple him or force him to become subservient to their national interests there is little else he can do. His main military forces are either under the thumb of the Syrian Army in eastern Lebanon or scattered among the eight Arab nations that took them in when they were evacuated from Lebanon.

The only strategy left, some senior PLO officials say, is to play for time, hoping that in the end the rebels' lack of momentum or popular support will convince them--and Assad--that their gambit failed. Then, they hope Arab mutual interest will lead to a rapprochement between Arafat and Assad.

"This mutiny, if that is what you want to call it, has gone nowhere," said Khaled Hassan, one of Arafat's senior advisers and a member of Fatah's central committee. "We believe the differences between these rebels will soon appear on the surface when they realize that they have just been used as tools of Syrian policy. Then they will fight each other and that will be end of this sad affair."

"Whatever the outcome is, and I believe that Arafat will win out as he has so many times before, we have already discredited ourselves by spilling blood among brothers," a Palestinian journalist, lamented over a beer at his hotel. "I'm afraid that once again we are proving to be our own worst enemies."