NO MATTER WHAT Egyptian President Anwar Sadat tells the Israeli parliament this morning, it is clear beyond cavil that his trip to Jerusalem has utterly transformed the psychological setting in which the Arab-Israeli dispute has been frozen for the past three decades. And while none of us can be sure of what specific results will ensue, we can all be certain that an opportunity has been created in which all the parties - the Israelis, the Egyptians and the other Arabs, too - can and must review virtually every diplomatic option and every political maneuver they considered in the past. For offers and concessions and tradeoffs and gestures considered unthinkable in the old psychological atmosphere become thinkable in the new. This sense of rare new possibilities is, if you will, Mr. Sadat's gift to the Mideast.

Now, of course, Mr. Sadat cannot bestow the prize of his presence on Israel, in Jerusalem no less, without appearing as the spokesman for all the Arab countries, not just Egypt alone. We take this for granted. More important, we assume that Egypt and Israel take it for granted. Not to make this assumption is to say that Mr. Sadat and Israeli Prime Minister Menahem Begin are very foolish, not to say irresponsible, leaders, who have surrendered to a theatrical impulse without having thought their venture through.

But is it possible that they would have secretly undertaken the planning for this departure last summer, months ago, as they did, without having some idea of how it would unfold? Surely they must have considered, specifically, what Israel needed from Egypt to win support in Israel's open society for any agreements ultimately reached. More to the point, both men must have thought about what Egypt needed from Israel to protect itself against the totally predictable charge that Egypt was being traitor to the Arab cause. Surely the Israelis realize that an immense part of ensuring that an Arab with whom they make a deal survives it is to give him a deal that he can defend against the hostility of other Arab countries. The length of time in which the mission was planned and what we believe to be the deadly seriousness of both Mr. Sadat and Mr. Begin - their commitment to the best interests of theire war-weary people - argue for granting them the benefit of the doubt.

Does Mr. Sadat have to be warned that he has taken a staggering risk? Do the Israelis need to be reminded that their self-interest demands that they "reward" the first Arab country to deal directly with them, the better to tempt other Arabs? We think not. Mr. Sadat and Mr. Begin are serious men.

There is another factor. Mr. Sadat, to spare himself Arab attack, could have waited until a Geneva conference to press his various claims. Obviously, he thought he could do better - for himself and, presumably, for his fellow Arabs - by making his own direct overture to the Israelis. We think it a mistake to conclude, however, that his choice reflects a failure of American diplomacy. For it was American diplomacy that gave thrust and focus to a settlement drive that, without the American impetus, the parties were demonstrably unable to generate on their own.

True, some American diplomats do appear a bit miffed that their pet Geneva project has been pushed at least temporarily out of the spotlight. But Geneva was never meant to be more than a means of bringing the parties together for face-to-face negotiations. If two of the parties have already begun their own negotiating process, then American diplomats, rather than fret that the parties cannot possibly manage without an American breathing down their necks, ought to see what help if any they can give to the negotiating process under way and stand ready to bring other Arabs so-minded to the negotiating table. And, as we said the other day, Washington must hold Geneva available as a safety net. There is nothing irreconcilable about direct talks between Israel and Egypt and a renewed Geneva conference. American officials, and, for that matter, Israelis dazzled by the Egyptian opening, should stop pretending that the two events are not inextricably linked in any realistic long-range effort to achieve a comprehensive Mideast settlement.

Peace cannot be made on one SUnday morning in Jerusalem. But peace can be made over time, we believe, in Jerusalem and Cairo and Damascus and Amman and, yes, Geneva. It can be made if Arabs and Israelis deepen and extend their direct relationship on the model that has now been set so courageously, and so respectfully, and so touchingly, by Anwar Sadat and Menahem Begin.