IN KNOCKING OUT the Iraqi nuclear reactor, the Israelis have made a grievous error. They did not act lightly, but they acted, we believe, in a way contrary to their own long-term interests and in a way contrary to American interests as well. They have validated -- revalidated -- the strategy of preemption, of which they may again be a sorrowful victim.No less significantly, they have validated -- revalidated -- the notion in Arab minds, and not only in Arab minds, that Israel is a nation that looks to make its way in the Middle East not by accommodation with its neighbors but by a policy of force.

They have further conveyed the idea that Israel, which is widely believed to have a nuclear capability of its own, regards itself as an exceptional state, one not bound by the rules and restraints applicable to its neighbors. They have confounded American strategy by issuing, in effect, an open invitation to the Soviet Union to reenter the region in the role of protecting innocent Arabs against American-sponsored Israeli assault. Finally and ironically, they have validated the idea that the kind of power that most counts in the Middle East is nuclear power -- otherwise, why would Israel have risked so much in this attack?

Yet this is also true: for more than two years, Isreal had been attempting, publicly and privately, to enlist the West's concern in its strategic nightmare -- that an Arab country, in this case Iraq, would acquire a nuclear capability. The source of its fear was a French-supplied research reactor, which runs on highly enriched uranium fuel directly usable in a nuclear weapon. The Israeli efforts to halt the French exports failed. The French felt their own interest in pursuing the export was of far greater importance than the consequences to others; and the Americans, despite intelligence estimates that Iraq was in fact pursing a bomb, were not prepared to really fight the French on that. Italian firms, it should be noted, had also agreed to supply Iraq with a small but militarily important reprocessing facility.

By last week, the fuel shipment, enough to make several Hiroshima-sized bombs, was imminent. Once that fuel was inside the reactor, it could not be attacked without risking release of large amounts of radioactivity and a consequent international uproar.If the reactor were quickly destroyed, however, there would be no risk of radioactivity and thereafter no legitimate reason to ship the fuel.

Thus a unique "window" opened. For a country convinced, as Israel plainly was, 1) that an Iraqi nuclear bomb was an intolerable threat to its vital interests and 2) that no relief from the West was forthcoming, the moment of truth had arrived. In those terms, the raid carries its own explanation: in effect, the so-called international community washed its hands and left the dirty work of stopping an Iraqi weapons program to the Israelis.

But these are not, finally, the terms in which the Israeli raid has to be measured. Many parties share the blame for the fact that Israelis and Palestinians remain at odds, but the Israelis must shoulder their own share. Especially under Prime Minister Begin, they have conducted a policy convincing most Arabs that there is no place for the Palestinians. This is not the whole explanation of it nor is it a justification, surely; but it is the atmosphere in which the Iraqi nuclear program has gone forward. It will resume or another Arab nulcear program will began unless there is a turn by Israel, with its Arab neighbors, toward a political approach. In raids on Iraqi reactors, as in raids on Israeli villages, there is nothing but more ruin.