Just over two months after Yasser Arafat's Palestine Liberation Organization left Beirut proclaiming that its confrontation with Israel last summer had given it new unity, internal differences and bickering are hampering the PLO's efforts to forge a new policy for the future.

PLO leaders, who insist that their organization must chart new policies following the organization's expulsion from Beirut, are locked in an intense, albeit publicly muted, debate. They are in disagreement about everything from Arafat's suspicions of Syria to the extent to which they should embrace the doctrine of "mutual recognition" with Israel implied in the peace plan proposed by Arab heads of state at their September summit in Fez, Morocco.

"Our battle with Israel this summer gave us a unity we never had before," said one member of the PLO executive committee last week. "But that was two months ago," he added ruefully, "and now many of the groups have fallen into their old habit of arguing among themselves -- not about the basics, but about secondary questions of tactics."

The extent of the PLO's internal disorder was underscored here at midweek when a meeting of its 15-member executive committee, chaired by Arafat, again failed to set a date and place for a meeting of the Palestine National Council, the PLO's parliament in exile. The council ultimately must debate and approve PLO strategy changes made necessary by the organization's forced evacuation from West Beirut.

Arafat has been promising to convene the National Council since he left Beirut Aug. 30, but differences among the executive committee have forced the PLO leadership to defer a decision on the meeting several times.

Instead of resolving the issue as PLO leaders had predicted before their arrival here for a two-day meeting at Arafat's new headquarters in a beach hotel outside Tunis, the executive committee decided to pass it on for debate to its broader Central Council at a meeting scheduled for Damascus, Syria, in two weeks.

The delay, according to a PLO communique, was to allow for "intensified discussions and consultations" among eight different Palestinian groups that make up the organization. These talks, the communique said, would be about the future policies the PLO should pursue in the light of "new conditions in the Middle East."

Even if some sort of consensus can be reached in the coming weeks on the differences roiling their ranks, executive committee members here now admit the meeting of the National Council may not take place before early next year -- although many hope it still could be held in December.

"All I can say is that the Palestine National Council will meet within two months," said Farouk Kaddoumi, head of the PLO's political department and the man who acts as the organization's foreign minister. "We did not decide on a date last week because it was necessary to have more dialogues."

While Kaddoumi and other PLO leaders interviewed here last week refused to be drawn into public discussion of the reasons more dialogue was needed, PLO officials in private admitted that there was no consensus among the organization's leaders and that until there was, there could be no open debate of PLO problems and policies before the 355-member National Council.

While one key issue under debate is implied mutual recognition between the PLO and Israel contained in the Arab summit Fez plan, PLO officials said in private that one of the main problems delaying the National Council meeting is the bad blood that exists between Arafat and Syria, which, as one of the PLO's most important Arab backers, wants to host the council meeting in Damascus, scene of the council's past two meetings.

Arafat adamantly has opposed meeting in Damascus, arguing that this would allow Syrian President Hafez Assad to exert undue pressure and threaten the PLO's much-cherished political independence. Arafat "suspects the Syrians of wanting to make the PLO nothing but an instrument of their national policy," said one PLO official here. "The chairman is determined not to let them do so."

That fear of Syrian pressure on the PLO is what led Arafat to set up his headquarters in Tunis, the seat of the Arab League, when he was forced to move from Beirut, his base since 1971. The decision was seen by Assad as a slap in the face because many PLO offices were already in Damascus, Syria had become the PLO's most important military supplier and Syria remains on the border of the Israeli-occupied territories that the PLO wants to liberate.

Arafat, however, never has forgiven Syria for sending its Army against his PLO units in Lebanon in 1976, when the Syrian forces entered the country to put an end to the 1975-76 Lebanese civil war. Beyond that, Arafat, who considers himself a moderate within the PLO, privately blames Syria for encouraging more radical Palestinian groups that are under its sway with mounting challenges to Arafat's policies and leadership.

Palestinians close to Arafat say that other reasons for his reluctance to moving to Damascus are his suspicion that Syria had a hand in the assassination -- widely linked to PLO renegade Abu Nidal -- of some of his Fatah representatives in Europe in recent years, and terrorist acts against civilians that have embarrassed the PLO's efforts to convince the world that it has renounced terrorism in favor of political action . Moreover, in Damascus, Arafat's security ultimately would rest not with his own men but with the Syrian intelligence organization controlled by Assad's brother, Rifaat.

As a result, Arafat has sought doggedly to get an agreement for the Palestine National Council to meet here in Tunis, where the Arab League moved its headquarters after leaving Cairo over Egypt's signing of a peace treaty with Israel.

With seven of the PLO's 15 executive committee members already living in Damascus, and with half of the PLO's eight member groups variously under Syrian government influence, Arafat has failed so far to win over his own executive committee to his point of view about the National Council meeting.

The decision to push the issue onto the Central Council and to have that group meet in Damascus -- under Arafat's chairmanship -- was clearly a compromise forced on the PLO chairman last week.

Aides close to Arafat, however, indicate that he may seek to have Algiers declared the site for the National Council meeting as a means of breaking the deadlock.

PLO leaders are also intensely debating the organization's stand on the Fez accords as well as what position they should adopt on President Reagan's Sept. 1 peace initiative. The Reagan plan, although falling far short of the PLO's minimum demands for an independent Palestinian state, has not been rejected officially by the PLO leadership because of its continuing hopes that it might yet be able to establish some sort of direct dialogue with Washington.

Although more radical groups are critical of the Fez agreement and urge an outright public rejection of the Reagan plan, PLO insiders remain confident that when the National Council finally meets, these issues will not divide the movement. The Fez plan, PLO leaders said, eventually will be approved by a resounding majority. They said they do not expect the PLO to vote on the Reagan plan as such, although heated criticism of it is expected.

"In the end the issue is more the PLO's relations with its own groups and with other Arab regimes like Syria that are the most critical issues right now," a senior Western European diplomat said in Damascus recently. "I think for all the internal arguments that are going on there is still general overall agreement on the PLO's aims. It is just the tactics that must be pursued to accomplish them that are once again being debated."