THE ISRAELIS, to judge by Ambassador Dinitz's article on the opposite page, reject a change in their West Bank position - no matter that the issue is hindering peace negotiations with Egypt and stiffening relations with the United States. Rather, the ambassador argues, attention should be turned to the Sinai, where, he says, his government has put forth a generous and eminently negotiable plan as a basis for peace with Egypt. The Egyptians, he concludes, have only to unhook their policy from Jordan for progress to unfold.

The ambassador clarifies a position that Israel feels has been widely misunderstood. We assume, furthermore, that Mr. Dinitz in his emphasis on the Sinai over the West Bank is raising the curtain for Prime Minister Menachem Begin, who is now expected to arrive in this country on Tuesday.

Well, why not a separate deal? What's wrong with a policy aimed at establishing peace on the most dangerous military front, a peace that could shower benefits on its makers and create conditions for further negotiations? The question becomes even keener when you consider that, if the Israelis did get Cairo on the hook, they would come under great self-imposed pressure to rethink those elements of their current Sinai position to which Egypt objects.

The answer lies here. Politically, and perhaps for personal reasons as well, no Egyptian leader can reasonably be expected to make a peace that smacks of selling out his fellow Arabs, in particular the Palestinians. Egypt may have no love for the Palestinians, and no desire for anything other than the rump Palestinian entity that the Jordanians and the Saudis and the Americans also favor, and no use at all for the Palestinian Liberation Organization. But it must make a fair gesture to the Palestinian cause, and it cannot do that while the Israelis refuse to consider West Bank withdrawal negotiable. If a demand on Israel for a general declaration of intent on withdrawal is an "unacceptable precondition," then so is a deman on the PLO to regard Israel as a legitimate state. Israelis aren't blind. They can recognize that. Politically they are not prepared or, as we would prefer to think, not yet prepared, to deal with it.

Mr. Begin arrives at a moment of high Israeli-American tension, enhanced by what might be called the frenzy of some American Jews. They feel - in the spirit of the Herblock cartoon today - that the Carter administration is beating up on Israel. They are attacking particular personalities in the administration, as though there were not a unified, presidentially directed policy, and openly threatening Mr. Carter with vengenace at the polls. To those who feel that way, we would merely note that the administration's disagreements with Mr. Begin are serious and principled, and that they have some of the substance but none of the intensity and anguish of the criticisms leveled at him by an increasing number of Israelis at home.

The issue here is not American pressure. The issue is whether Israeli government can be sure it is exhaustively exploiting the possibility of peace that Anwar Sadat opened last November. No fair-minded person can deny that Menachem Begin responded in a manner surpassing what his precessors' pllitical record and his own personal record led one to expect. The current focus on a Sinai settlement represents a very great degree of innovation and risk-taking on Israel's part.

No matter how far Israel, as well as Egypt, has come, however, the crux is how much farther the two sides must go if the peace prospect is not to spin away in the sands. The administration would be unforgivably negligent if it offered anything less than its best judgment. It cannot responsibly offer support, or even tolerance, of a concept that it feels leads to a dead end. Deeper Israeli contemplation of the West Bank territorial issue is, we are convinced, unavoidable if Israel is to get the crack at negotiating the Egypt-first settlement that it craves and deserves.