THE WAY the Israeli government chose to mark the first anniversary of the Camp David Accords -- by deciding to let Israelis start buying private Arab land in the West Bank and Gaza -- is troubling on several counts. First, it is the latest in a series of acts foreshadowing a permanent Israeli presence in the occupied territories and facilitating Israeli settlement there. As such, it is bound further to discourage Palestinian participation, which has been nil, in the talks aimed at setting up Palestinian self-rule. It cuts directly across Jerusalem's Camp David pledge to leave the "final status" of the West Bank open to negotiation. It is, in brief, a blow to Camp David, or at least to the conception of Camp David that reasonable people outside Israel have in mind. Egypt's vice president made the point fairly and soberly in a White House visit yesterday.

Beyond that, the new cabinet decision has about it the look of a certain deliberate challenge. It is as though the Israelis are indirectly taunting Jimmy Carter, doing something that they know he would object to but which they feel he lacks the political clout to do much about. In this they may well be right. In failing to extract a firm no-settlements pledge from Menachem Begin at Camp David and in declining to do more than slap IsraelS wrist for its subsequent settlement moves, Mr. Carter contributed to the disarray of his own policy. And his general political situation is now such that he cannot easily bring heavy artillery to bear. Yet the Israelis, by seeming to take advantage of Mr. Carter, risk stirring another current of American feeling. They should not be drawing down so casually their still-considerable but depleting reserves of political capital in this country.

Look at it this way. The Palestinians are coming -- in public opinion in the United States if not yet in direct official policy. What the Israelis need most from the United States is not weapons and dollars but help in reducing Palestinian demands to proportions that Americans can in conscience ask Israel to accept. A week ago, for instance, the PLO's Yasser Arafat, lying, told an American TV interviewer he could not "remember" the provisions in his organization's charter calling for the elimination of Israel. It is precisely to help expose the PLO in lies and feints like that, to tame it, that the Israelis desperately need full American cooperation. But cooperation must run both ways. Opening up the West Bank to private land purchases is not cooperation. It is sand in the gears.