For the first time since Egyptian President Anwar Sadat began his go-it-alone diplomacy, the Palestine Liberation Organization appears to be convinced that no quick settlement at its expense is likely, PLO sources said today.

Thanks to a combination of what the PLO views as Israeli instransigence and President Carter's verbal blunders, Sadat "now finds himself back at square one," much to the PLO's relief, the sources added.

Even if Sadat's original timetable has been slowed down, the sources still fear that he may make a separate fear peace with Israel, in which the PLO would be the principal victim, rather than admit failure.

In PLO eyes, positions taken by Israel and the United States at the least have destroyed Sadat's tactical efforts to win moderate Arab support by claiming that he was demanding total Israeli withdrawal from occupied Arab lands and respect for the Palestinians' national rights.

Carter's brief stopover to see Sadat on Wednesday is not expected to change the Egyptian president's predicament, the sources said, "although it may make him happy for a few days."

They reasoned that barring a major shift and thereby risking angering the Israelis, there is little Carter can do to repair the damage inflicted on Sadat when Carter's remarks last week were interpreted as opposing the creation of an independent Palestinian state on the Israeli-occupied West Bank of the Jordan and the Gaza Strip.

At best, the Palestinians expect Sadat to ask for American support in forcing Israeli concessions on the Sinai. There, Israel both refused complete withdrawal of its own forces and insisted that the Egyptian military not advance beyond its positions astride the Mitla and Gidi passes in the western Sinai.

Some Palestinian sources even suggested that Carter's remarks were purposely calculated to both embarrass Sadat and "cut him down to size." This view assumes continuing American unhappiness with Sadat's brand of direct negotiations, which has left the United States, and other powers, with a diminished role.

In any event, alleged Israeli intransignece over the Sinai is seen as a major reason why Sadat still keeps the door open for an overall settlement, the sources said.In turn, that explains why the PLO itself has eased its once strident charges of "treason" in describing Sadat.

For propaganda purposes, the villains are the same old ones, the classic suspicion of U.S.-Israeli collusion, fueled by Carter's recent remarks make Sadat out as an unwitting tool of a "Zionist imperialist conspiracy."

Despite Sadat's reiterated criticism of the PLO, it has maintained discreet, high-level, unofficial contacts with him.

"We want to do nothing to let anyone claim we are a bunch of crazies," the sources said.

The PLO is so weak, however, that the leadership can still only hope that the Sadat initiative will fail and that a reunited Arab world will return to the comprehensive settlement plans once associated with the now sidetracked Geneva conference.

That was apparently one of PLO leader Yasser Arafat's main aims in a recent interview with the Manchester Guardian in which he sought to show PLO reasonableness.

Referring to the joint U.S.-Soviet declaration of Oct. 1, which raised Israeli hackles, Arafat said "In spite of certain reservations" it "was acceptable to us."

Even PLO threats against American interests in the Middle East were put into perspective by Arafat. Asked if he meant sabotage against Middle East oilfields, he replied: "I am not talking about these things, but they (the Americans) have to understand that nobody can say farewell to the PLO without jeopardizing his own interests."