Faced with what they consider Israel's unalterable determination to leave them no honorable retreat from Israeli-surrounded West Beirut, Palestinian guerrilla leaders tonight reportedly had resolved to hold their ground and were prepared for a new round of fighting.

A central committee meeting of Fatah, the mainstream guerrilla organization that is Palestine Liberation Organization Chairman Yasser Arafat's power base, decided to make no more concessions to the Israelis, informed Palestinian sources told The Washington Post.

That position was made today before Israeli Prime Minister Menachem Begin, in a speech before the parliament, said that the guerrillas would be permitted to carry small arms with them as they leave the Lebanese capital, something that Israel previously had said it would not allow. There was no immediate Palestinian reply to Begin's statement, which appeared to amount to a first, small concession.

In the earlier conversations, the Palestinians freely admitted that they were playing for time. But they appeared convinced that a ground attack against their positions in beleaguered West Beirut would prove too costly for Israel to contemplate in terms of its own potential casualties and world public opinion.

In the midst of conflicting reports about the Palestinian leadership's real mood and intentions, it was difficult to determine whether the latest reported Fatah position was part of the bargaining process--and Begin's later statement a bargaining reply--or a final decision by the guerrillas to stand fast. The bulk of the evidence suggested that the latter was more likely the case and was the result of a detailed examination of the remaining options available now to the guerrilla movement.

While the sources still held open the possibility of a Palestinian departure from Beirut, provided the Israelis softened their terms, they said Fatah leaders were far from ready to accept the "unconditional surrender" Israel had been demanding of them.

Aside from the perhaps lesserquestion of carrying light arms along on their exodus, the main Palestinian sticking point was said today to be the maintenance of a small armed Palestinian presence in Lebanon. Although the force would be under Lebanese Army control, it is something that the PLO regards as central to its survival in a hostile environment.

Palestinian officials with knowledge of the PLO's diplomatic traffic maintained that the United States, despite Alexander M. Haig Jr.'s resignation as secretary of state, was continuing to maintain multiple channels of often contradictory communication.

These officials specifically mentioned an unbending State Department position, all but indistinguishable from that of Israel, concurrent side channel traffic between national security adviser William P. Clark and Saudi Arabia and still other communications with France seeking to cast the PLO leadership in a compromise-seeking posture.

The Palestinian officials openly acknowledged that their main policy was playing for time in the hopes of a miraculous reversal of their present dim prospects.

Apparently inconclusive meetings continued throughout the day and night, involving Lebanese Prime Minister Shafiq Wazzan, Foreign Minister Fuad Boutros, Army intelligence chief Johnny Abdo and former prime minister Saeb Salam. Salam also met with Arafat.

The Palestinians hoped to boost support among their fellow Moslems in Lebanese politics--especially Salam--for a continued military presence here. They believe that is essential to keeping the PLO alive as a viable political force.

But little, if any progress, on that score with even their political friends in Lebanon was reported.

Internationally, the Palestinians appeared convinced that the strains of the war were beginning to tell on Israeli public opinion, not just because of the massive economic and financial drain on the Jewish state, but because of the prospect of heavy casualties inherent in any ground assault.

But, if the Fatah central committee meeting was an accurate reflection of the overall Palestinian mood, the PLO believes that more fighting is preferable to having its forces scattered abroad and the leadership submitted to the political line dictated by Syria, Egypt or any other Arab countries where refuge might be found.

The subliminal message was that the Israelis were forcing a military showdown and that a renewed round of fighting might shock Saudi Arabia, Egypt or any other well disposed Arab countries into taking dramatic action against the United States. Any such pressure then might force what the Palestinians see as American duplicity into the open and finally bring the Reagan administration to put pressure on Israel.

Meanwhile, American special envoy Philip C. Habib was reliably reported to be frustrated and complaining openly that he had been cast in a thankless role that he had not expected to play.

While much of the world remained convinced he was an active mediator in the complicated four-way dealings among Israelis, Palestinians, Lebanese and Americans, he was said to have told a visitor "I am not a negotiator."

Caught in a moment of apparent depression in the Israeli-controlled hills overlooking threatened West Beirut, Habib said, "What negotiations?" He was reported to have added that he was reduced to the role of a postman, passing on Israeli demands and Palestinian counter proposals.

Among his frustrations was reported to be Palestinian failure so far to respond to questions he addressed to the guerrilla leadership almost a week ago.

As reported in the Lebanese press he had asked whether the PLO had agreed to abandon all its military prerogatives in Lebanon, agreed to accept Lebanese sovereignty and surrender its previous state-within-a-state status.

Meanwhile, distant explosions were heard in Beirut, apparently coming from the mountains east of the capital where unconfirmed reports said Israeli artillery was shelling Syrian positions near Hammana.

And as Israeli psychological pressure on West Beirut continued, more Lebanese families drove across the only crossing point to safety in Christian East Beirut. The Phalangist militia announced that all Lebanese--but no Palestinians--would now be welcome in their territory.