THERE IS A sense in which the parties to the Beirut drama have become prisoners of a tragic irony. Civilized people and nations could not fail to protest the carnage being inflicted by Israeli guns. But those very protests, encouraging the PLO to hang on and thus stir Israel to press harder, may have increased the casualties. For the PLO did, as the Israelis charge, take Beirut hostage. The Israelis did then, as always, refuse to bend to hostage-taking. President Reagan found himself in a hopeless contradiction, endorsing Israel's goals but attempting to control its tactics. In the circumstances, the Israelis were virtually bound to take his first message as a license and to try to undo the impact of the second by demonstrating their uncontrollability. The city is paying the terrible price.

Long after some sort of settlement has been reached, the argument will burn on as to whether a concern for casualties finally diminished or expanded the toll and finally expedited or delayed the settlement itself. At this point, our own judgment is that Israel greatly overreacted to the prospect that the PLO might parlay American jitters into a permanent lease in Beirut. The Saudis, Syrians and other Arabs have been determined for some time to remove the PLO from Lebanon. What is now needed is not more Israeli pounding but enough of a respite to let American diplomacy take advantage of the pounding already delivered.

However the Beirut crisis winds down, Israel's position in American public opinion has been, we believe, transformed. The erosion that was under way as a result of its West Bank policies has been propelled forward by its conduct in Lebanon. The easy assumption of Israel's higher moral standard, a tremendous asset, is a casualty of Beirut. Even those who accept the rationale for the Israeli thrust and/or those who are prepared to turn it to good effect have been appalled by the spectacle of torn bodies and devastated streets. Others have been sobered by the spectacle of Israel's seeming defiance of American sensibilities, American strictures and American interests. The general feeling is, as we perceive--and share--it, that the situation in the Middle East cannot be allowed to go on as it has in the past.

That requires action on two fronts, the Lebanese and the Palestinian. The requirements in Lebanon are relatively clearcut. Fortunately, Lebanon has the native talents and the friends with means, including the United States, to begin the physical rebuilding promptly; in southern Lebanon it has already begun. The political rebuilding is harder. A theory is current that there is no Lebanon, that the place is split too many ways and is incapable of self- rule. The theory patronizes the Lebanese and, too often, masks an urge to establish Israeli hegemony, partly by occupation and partly by manipulation of local clients. The Israelis are preparing the infrastructure (new roads, a trading net, an administrative apparatus) and the rationales (local disorder, Maronite insecurity, the Syrian presence) for an indefinite stay. It is absolutely wrong. It may be too early for the Lebanese to say just how they intend to put their country back together, but it is not too early for everyone to be alert to Israel's evident designs.

Is there anyone now left who does not understand that the Lebanon crisis was in the first instance a product of the unresolved Palestinian crisis? Every sensible person knows the answer: to establish a home for the people who, for many reasons, not least their own errors and omissions, got no home when Israel was founded in 1948. Every sensible person also knows the method: a negotiation in which the two parties participate and their patrons accept their responsibilities. Strangely, the Palestinians' several patrons may be readier than Israel's one patron, the United States.

For the United States to do what has to be done will take immense courage and steadiness. But for the Reagan administration to shy from the task would be an immense dereliction of duty and interest. Only one course can conceivably redeem the tragedy of Lebanon: to ensure that the Lebanese, Palestinians and Israelis come to peace.