THE ADMINISTRATION reports that it has cracked the SALT II case. Yesterday, to mark what he described as the conclusion of negotiations between Soviet Ambassador Anatoly Dobrynin and himself, Secretary of State Cyrus Vance - along with Defense Secretary Harold Brown - affirmed his confidence in the treaty that is being negotiated and which is evidently much nearer completion now that the U.S. and Soviet delegations in Geneva have been instructed, as Mr. Vance said, to "incorporate into the joint draft treaty text" the agreements he and Ambassador Dobrynin reached. Apparently some of this agreed material involves language already drafted, and some of it involves principles still requiring to be put into specific treaty terms. There also remain what were called "secondary" issues to be negotiated out in Geneva.

What have we got here? Not a treaty - that is the first thing to be understood. We have got what the administration regards as major and probably critical administration regards as major and probably critical progress toward the completion of a treaty. But there is as yet nothing to be initialed by representatives of the tow countries. Until there are such documents, the debate must remain in the realm of shadow play. Secretary Vance said, in his White House remarks, that what has been agreed to so far embodies some fine principles and purposes. He asserts that the treaty will establish limits on numbers of strategic nuclear weapons, begin reducing their high levels and constrain the race to improve them - and that this country's securtiy and the stability of the strategic balance between the United States and the Soviet Union will be served in the process.

Anyone who could be against that formulation is just plain against arms-control deals of any kind with the Soviet Union. The trouble is that the real test of a SALT II agreement does not lie in the admirably stated principles and assertions, but rather in the way the concrete terms of the treaty itself and its accompanying protocol reflect the objectives involved. It is of course true that on the basis of this information some senators have already let it be known that they don't think the deal being made is safe enough or good enough. But their opposition is as premature at this point as hallelujahs would be.

In our darkest fantasies we sometimes suppose a SALT II drama playing out in which the process, having been "kicked off," as they say, a few weeks back without a treaty goes forward all through the summer and fall, complete with heated, even anguished and passionate debate . . . and suspense and the rest and, finally, a Senate vote and then ratification - and then someone remembers that there still isn't a treaty. All right: It probably won't come to that. But it is worth pointing out that whereas - if we may use a little treaty language ourselves - it is good and heartening thing that the administration believes it had brought the country to the verge of a truly beneficial strategic arms control treaty, it will be an infinitely better thing if and when it does.