The "secret" that mischievous Mikhail Gorbachev revealed at the Helsinki summit was the unconcealed and well-known fact that for years the United States had tried to fence the Soviet Union out of the Middle East. Now George Bush confirms that Moscow is in and formally commits the United States not only to deepen superpower cooperation in the Persian Gulf but to work together ''to resolve all remaining conflicts in the Middle East. . . ." This consummates a major turn, and Gorbachev is justly pleased with it.

But is it not also something worthy of more universal celebration, something promising not just a unilateral Soviet gain but advantage all around, especially in the Arab-Israeli dispute? This is precisely the prospect held out by Gorbachev's "new thinking" on the Middle East, where for years the superpowers have taken divergent and competitive tacks.

Some part of the answer will come as the Gulf crisis unfolds. Gorbachev's commitment to end it on United Nations terms through a political process is no less important to his prestige and future policy than Bush's commitment to make sure, as he told Congress, that "Saddam Hussein will fail." The one leader has invested in a method, the other in an outcome: this is the silent tension under the dazzling surface of their accord.

But scarcely had the summit ended when former Israeli prime minister Yitzhak Rabin went to the quick. In Washington to address the American Jewish Congress, he suggested that Bush, notwithstanding his explicit disavowal of direct linkage of the Gulf to the Arab-Israeli conflict, was now contemplating, with the Kremlin, "phased linkage." No, thundered Rabin, this would reward aggression; it will lead to a big Soviet-favored international conference at which Israel will be pressed for withdrawal under a U.N. resolution (242) that does not distinguish between territory acquired by aggression (Kuwait) and territory acquired in reaction to aggression (the West Bank).

Rabin and others for whom any hint of linkage is poison are right to suspect that the Bush administration connects the Gulf and the Palestinian question. Indeed, Gorbachev spoke for many Americans when he said that stalemate on the latter ''bears on the acuteness'' of the Gulf crisis. Demonstrably, Saddam is a hero in large swaths of the Arab world by virtue of painting himself, however improbably, as the Palestinians' champion.

Aaran Miller of the State Department presented a policy planner's view to the same Washington conference addressed by Rabin. He said that reviving the American-sponsored Israeli-Palestinian peace process -- which Israel had backed out of even before the Palestinians' hailing of Saddam further curdled the Israeli taste for dealings with them -- was even more necessary now as an alternative to Saddam's way of intimidation and brute force. Operationally, he said, there could be no linkage; ''analytically,'' it could not be denied.

An echo could be heard a few days later from a Soviet diplomat who observed that ''dialectically'' a linkage was evident. A logic runs, he offered, from the welcome Bush now gives Moscow as a partner in a Mideast regional security structure, to eventual joint Soviet-American engagement in the Arab-Israeli issue.

The American and Soviet diplomats are thinking, if not yet in unison, then in parallel. I find what they say persuasive. On the American side at least, an interest in Palestinians is not the wanton and misguided obsession that Israeli regulars say it is. It is a key to regional stability and it is the essential condition to calming the political inflammation that most threatens Israeli wellbeing, with or without Saddam Hussein.

Certainly the latest double shock of Iraqi aggression and fervent Palestinian support for it compel understanding for Israeli misgivings about being hustled into a bad deal by an American administration bent on accommodating Gorbachev on the one hand and competing for Palestinian favor with Saddam on the other. The right response is a patient, purposeful American diplomacy that recognizes Israeli anxieties but is not paralyzed by them.

In such an enterprise, a Kremlin that is proving its regional credentials in the Gulf could be a useful partner. The Soviet Union, after all, has already moved far from its former rote backing of an unreconstructed PLO. It has moved into a complex pattern of relations with Israel, including moderating Syria, now resisting Iraq and meanwhile providing something more treasured by Israelis than all of their American aid -- immigrant Jews. Americans and Israelis would be foolish to ignore the possibilities that open from Gorbachev's ''secret.''