Just when the Palestine Liberation Organization seemed to be making progress toward its goal of achieving a diplomatic opening to Washington, a well-meaning but overeager U.S. congressional delegation appears to have dealt that goal a setback.

Although PLO history is strewn with the wreckage of just such misunderstandings involving journalists, visiting dignitaries, Arab leaders and, on one occasion, Secretary of State Cyrus Vance, this time Arafat does not appear to have fallen victim to his own legendary hesitations and obfuscations. The facts, such as they are today, suggest that Arafat was more sinned against than sinning.

Rather, the confusion was generated by his congressional visitors, especially Rep. Paul McCloskey (R-Calif.), who appear to have harmed the very cause they--and Arafat--hoped they would promote by coming to Lebanon.

By claiming that Arafat had signed a statement recognizing Israel's right to exist, McCloskey argued that the time had come for the U.S. government to deal with Arafat.

That certainly was and remains Arafat's goal, the political compensation--some might say cover-up--for the clear military defeat the PLO has suffered since the June 6 Israeli invasion of Lebanon.

But as the videotape of Arafat's encounter with the congressional delegation clearly suggests--and as the testimony of Rep. Nick Rahall (D-W.Va.) confirms--the Palestinian leader never encouraged his American guests to think he was about to recognize Israel on the terms they outlined.

The whole misadventure, if anything, has sidetracked whatever small progress the PLO thought it had been making in improving its image with the Reagan administration now that Alexander Haig, whom Palestinians considered a surrogate Israeli, has been replaced by the apparently more even-handed George Shultz as secretary of state.

Within an hour of Arafat's televised encounter with his congressional visitors, an authoritative Palestinian official felt obliged to cross the T's and dot the I's that Arafat traditionally has preferred to leave murky .

Reviewing the PLO's unbending policy, the official said, "When we get a state, we will recognize Israel," but he warned that the guerrillas would not yield their trump card as a unilateral concession.

"The PLO will make this concession" of recognition, he said, "only for an equal concession--self-determination, i.e., a state--not for the privilege of talking to the U.S.A."

Talks in Washington last week between American officials and the Saudi and Syrian foreign ministers, and, through intermediaries, with PLO emissary Khalid Hassan, had raised hopes for just such a dialogue.

Although the discussions appeared far less fruitful than PLO optimists had hoped, nonetheless the very presence of a senior PLO emissary in Washington would have been unthinkable in the Haig era. PLO officials must have realized that Shultz could not reasonably have been expected to open a dialogue with the PLO overnight.

Ever since September 1975, when Secretary of State Henry Kissinger signed a secret annex to the Sinai II disengagement talks between Egypt and Israel, successive American administrations have interpreted in the strictest possible fashion a promise not to deal substantively with the PLO until the guerrillas recognized the Jewish state's right to exist.

PLO optimists and realistic Mideast analysts therefore argued that only after the PLO had proved its good faith by actually starting to move out of besieged West Beirut and Lebanon could the Reagan administration be expected to reward the guerrillas with such a political compensation.

Israel's government has proved reticent enough about granting the PLO a face-saving token withdrawal from West Beirut without asking Tel Aviv to swallow the infinitely more worrisome inauguration of direct dealings between its arch-enemy and its principal major ally.

Nonetheless, Arafat's efforts to flirt with Washington were interpreted here--and in Israel--as signals to the Reagan administration that in the right conditions he would take the plunge and agree to the "mutual recognition" that his supporters have favored increasingly.

Uri Avneri, the former member of the Israeli parliament and gadfly magazine publisher, the PLO's own "peacenik" Issam Sartawi, former French premier Pierre Mendes-France, Nahum Goldman, life president of the World Jewish Congress, and Philip Klutznick, honorary international president of B'nai B'rith, in recent weeks have all spoken out along these lines.

Such encouragement of the moderates inside the PLO is not to the liking of Israeli Prime Minister Menachem Begin and Defense Minister Ariel Sharon, the architect of the present invasion.

Stymied for the past six weeks at the gates of West Beirut, subject to increasing criticism that now is beginning to reach the officer corps of the Israeli army, the last thing they want is anything smacking of a PLO political victory salvaged from the guerrillas' military humiliation.

Israeli Foreign Ministry spokesman Avi Pazner was quoted by the British Broadcasting Corp. today as saying he did not think the Begin government would recognize the PLO even if Arafat did recognize Israel's right to exist, because the present guerrilla leadership's "hands are stained with blood."

The McCloskey incident here has made it improbable that Begin will be faced with such a dilemma in the near future.