MENACHEM BEGIN got out of a hospital bed

Monday and, within hours, without a word of notice or preparation, broke the fundamental Israeli promise on which all of Israel's hopes for peace hinge. That promise, repeated many times, was to exchange territory for peace. By annexing the Golan, Israel precludes peace with Syria. It is that simple.

Prime Minister Begin offered two lines of argument. First, he says, Golan is part of the historic "land of Israel." But it is part only of what he calls, and then only in his less guarded moments, eastern Eretz Israel, which stretches from the Jordan eastward to the Euphrates River. It is a stroke of sheer fanaticism to base an actual territorial claim on that fantasy.

Then, Mr. Begin says, there is security. Yes, there is. Israel needs security from attack by Syria, which sat on the Golan and poured fire down on Israeli farmers before 1967 and which has refused to accept Israel and negotiate peace ever since. Syria meets no acceptable standard of international comity. Internal tensions have made the Syrians especially nasty in recent years. Ultimately, nonetheless, security for Israel rests on waiting for Syria to come around. Certainly the answer is not to make it hard for Israel's friends to justify or support Israeli conduct.

The most damaging burden Washington carries in its dealings with Arab countries is their suspicion that the United States is an accomplice, either mindless or witting, of a manipulative Israeli expansionism. This is why the administration must leave no doubt about its rejection of the Israeli action. Defense Secretary Caspar Weinberger says it is like the Israeli attack on the Iraqi reactor. Wrong: it is worse. The attack on the reactor had a certain security rationale. This step has none.

Fortunately, it is only a political decision, changing nothing on the ground. Therefore, a political decision can rescind it. Mr. Reagan should not bother tut-tutting. He should bring real pressure to bear on the Israelis to return to the position that territory is to be traded for peace. There is nothing to negotiate here. It must be, for the United States, a point of principle. What other basis is there on which the United States can support Israel?