THE IMPORTANCE of President Anwar Sadat's declaration that he's ready to go to Jerusalem to talk peace can scarcely be exaggerated. He could not, by such a trip, cut through three decades of Arab-Israeli distrust. But he would finally be addressing what is, in the minds of many Israelis, the greatest obstacle to peace: Arab rejection of Israel's right to exist.

The principal evidence cited to prove this point has been the Arabs' refusal to start opening the contacts that Israelis (and Westerners) take as the normal stuff of good neighborly relations. A corollary claim has been that Arabs make moderate statements only for foreign consumption. In defense, some apologists have claimed that Arabs, for the deepest cultural reasons, could not reasonably be asked to accept Israel's right to exist; at most, Arabs might grant Israel token contact as a last step in a neutral political deal.

Yet President Sadat now has said, in public, to his parliament, that he would go to Jerusalem itself, and his audience wildly applauded. Was it a meaningless gesture, merely a piece of political theater? It could be asked just as reasonably whether Israeli Prime Minister Menahem Begin's prompt invitation to Mr. Sadat was sincere. For even as Israelis have ached for the direct contact that Mr. Sadat now dramatically offers, they have known that such an offer would put Israel under pressure to make matching concessions. In a real sense, Arab intransigence has been a solace to Israel, sparing it hard choices. The Sadat initiative will cause genuine uncertainly among the many Israelis surprised to see an Arab take the sort of step they have long defined as the essence of peace.

Mr. Sadat's political courage and imagination, working in a context of economic and social crisis, are chiefly responsible for his latest initiative. They illustrate, too, that the administration's wobbly but principled reach for a settlement is opening vistas unexpected even a few months ago. Egypt is leading the public part of the Arab movement toward Geneva. Syria, though with some strong reservations, is also engaged. Their leaders are about to meet for the crucial task of inter-Arab coordination. The United States, meanwhile, is trying with new pressures and reassurances to embolden Israel to respond. The Arab states are ready to sit down with the Israelis, the Israelis are ready to sit down with a Palestinian representative and the Arabs are hunting for a Palestinian acceptable to the Israelis. The remaining difficulties on the substantive issues are immense. But the promise is immense, as well.