YESTERDAY'S WHITE HOUSE announcement of an American-Israeli-Egyptian summit meeting on Sept. 5 at Camp David is good news - in a strictly limited sense. That is to say, it is good news only because just about any other conceivable next step in the Mideast peace effort would have been worse. It is almost a cliche by now to speack of a "critical turning point" in the Middle East, but the current condition surely qualifies. The evidence of disintegration is everywhere: in the breakdown of negotiations, the harsh polemics from Cairo, the political discord in Israel, the divisive tugging and hauling among the Arabs. It is evident even in the stated purpose of the September summitry: "to seek a framework for peace." To talk of a mere "framework" is pretty thin gruel when you think of all the heady things that have been said - and done - in the nine months since Egypt's President Anwar Sadat launched his peaced initiative in Jerusalem. But we would argue, on the contrary, that to have projected any more specfic or ambitious objective would have been, at the very least, disingenuous.

We do not mean by this to denigrate the accomplishment of President Carter and his secretary of state, Cyrus Vance; only a few days ago, Mr. Sadat seemed to be unwilling to resume negotiations in any form. Nor would we rule out the possibility that a high-pressure meeting of the top men may not be just what's needed to wring the sort of concessions from both sides that will be needed to break through the current impasse. The point is simply that while this sudden scramble for the summit is almost certainly prudent and essential - and perhaps even a master-stroke - it is also exceedingly perilous. It can be all these things at once, and for the same reason: the absence of a visible, acceptable alternative. If the lack of a promising alternative is what made a summit meeting inescapable in August, you do have to ask yourself what alternative there will be a month or so from now if this almost desperate rescue operation fails.

One answer is that the absence of a safety net - some clearly recognizable and foreseeable next step after Camp David - is precisely what can be counted on to concentrate the minds of the principal participants and to ensure at least some limited success. But this is also, of course, what gives the meeting at least the appearance of a high-risk, last-chance affair. There is precious little evidence that Mr. Carter has in hand commitments from both Israel and Egypt to at least some minimum achievement at Camp David. Clearly there has not been the sort of careful preparation at lower levels that traditionally has preceded most summit-level encounters in the past. It is not apparent, in short, that by conventional standards the Mideast dispute has been made safe for summitry in the sense that anybody has any firm idea of the terms or the elements of a successful outcome.

And this, in our view, is a powerful argument for not investing this particular summit with the aura of a Great Event - for not looking too hard for big break-throughs or for agreements on specific, substantive questions of any kind. The Carter administration is offering modest hopes of "narrowing differences," of the "removal of obstacles," of seeking to establish some more stable and consistent process for resuming the long, hard bargaining that will be necessary to reach even limited settlements. And that sounds about right to us. To expect some new "Spirit of Camp David" to bring quick movement to a Mideast settlement is not to have noticed what happened over the last nine months to the "Spirit of Jerusalem."