DR ISSAM SARTAWI, one of the few moderate voices left in the ranks of the Palestine Liberation Organization, was shot to death in the lobby of a Portuguese hotel last week, the victim of an extremist assassination plot. Gloating over their gruesome triumph, the conspirators, based in Damascus, told the press that "it is our pleasure to Communicate to you our success in implementing the death sentence towards a criminal and a traitor." Sartawi died because he had the guts (or perhaps the foolhardiness) to suggest that his organization recognize and come to grips with a political entity that will always be firmly rooted in the Middle East-the state of Israel.

PLO Chairman Yasir Arafat, living in the dream world that Sartawi disdained, deserves much blame for this latest outbreak of hit-and-run political murder. True, it was a splinter faction led by one of Arafat's worm enemies that ordered the slaying and took credit for it soon after. But it was Arafat himself who had effectively undermined Sartawi's already slim chances of survival last February when he abruptly removed the doctor from the speaker's list at the Palestine National Council meeting in Algiers and then ejected him from the session entirely. Arafat made it clear to every delegate present that Sartawi's brand of diplomatic realism would never be welcome. The charter ideology of the PLO, after all, remains committed to the annihilation of the Jewish nation.

Arafat has made a career out of sabotaging reasonable proposals. The latest victim: President Reagan's Middle East Peace initiative. For all of its shortcomings, the President's plan represented the only viable hope of continuing the process begun at Camp David nearly five years ago. It was Arafat who foiled any chance of progress last week by refusing to approve official Jordanian participation in the talks. And Jordan's King Hussein, virtually held hostage in his own land by the intimidating presence of Palestinian guerrillas, would rather not join the ranks of the martyrs--men like Sartawi and Anwar Sadat, for example, who dared to break with the PLO leadership and pain dearly for their apostasy.

Most of the interested parties in this troubled region recognize that a lasting solution to the perpetual state of warfare requires the active participation of the Palestinians themselves. By the same token, surely Arafat must by now realize that no nation, let alone Israel, can afford to deal with a Soviet-equipped pseudo-military organization unwilling to bend in its insistence on total control over the West Bank and Gaza.

Yasir Arafat had the opportunity last week to dissociate himself from the mafioso style of politics that has long characterized inner PLO circles. Instead, speaking to reporters in North Yemen, the guerrilla chieftain, in an unfounded and preposterous charge, blamed Israeli agents for the Sartawi assassination. Despite such consistently irresponsible behavior, a number of European governments--Greece and Austria among-them--have established close relationships with PLO representatives. The PLO, they argue, should be welcomed into the diplomatic community by both the United States and Israel as the legitimate voice for Palestinian national aspirations.

ALL OF WHICH brings up an important lesson in political accountability. Last year, many of those same European governments insisted that Israel be held responsible for the slaughter perpetrated by Christian Phalangist forces in the refugee camps of Sabra and Shatila. Israeli forces, though not directly implicated, shouldered much of the blame in the world's press for the massacre, as it had indeed occurred under Israeli auspices. In accordance with a conscientious democratic ethic, Prime Minister Menschem Begin's government conducted a thorough investigation of the conduct of several cabinet ministers. It is a revealing if not pathetic comment on the state of international diplomacy that no official body, Christian or otherwise, was ever asked to scrutinize and publicly condemn the actions of the real murderers--the Lebanese Phalangists.

Similarly, would it be too much to ask that Yasir Arafat, as the self-proclaimed prophet and dictator of the Palestinian movement, take responsibility for Sartawi's murder--or, for that matter, for the slaughter of Israeli athletes at Munich in 1972? Should Arafat be made to answer for the lives of innocent civilians he expended as convenient air cover during the battle of Beirut, by cunningly hiding his men among them in hospitals and apartment buildings? Unfortunately, as an unclected leader. Arafat is free to do as the pleases. But if the PLO continues to claim sole authority as the legitimate representative of the Palestinian people, it should do their cause justice and conduct itself in accordance with the rules and etiquette of civilized diplomacy, not with those of organized crime. Evan T. Barr