IN HIS STATEMENT on nuclear power policy last week, the President seemed to back away from his own earlier tough stand on nuclear weapons proliferation - and, incidentally, from the tough stand taken by the Ford administration in a key policy statement last October. At least that is the most we can make of the President's statements and the rather muzzy background music that accompanied them: on-and off-the-record briefings, foreign government responses and the rest. The heart of the matter is this: Plutonium, a nuclear explosive, is created in the course of operating a nuclear power plant; and by the technology known as "reprocessing" it can be separated from the residue of the plant's spent nuclear fuel and used again as fuel - or , and this the point, used to make nuclear bombs. Up until last week Mr. Carter seemed much more determined than he does now to discourage our friends (and acquaintances) abroad from pursuing this extremely dangerous and ambiguous reprocessing technology, which cannot be safeguarded against misuse.

It is, of course, true that the President announced his attention to "defer indefinitely" this country's own pursuit of commercial reprocessing and to defer, at least for the time being while alternatives are explored, work on the plutonium breeder reactor. These steps were intended by him to demonstrate our own belief that the retrieval and use of plutonium are not essential to a well-functioning nuclear energy program, nor even necessarily sound from the economic point of view. And it is also true that Mr. Carter affirmed his discourage other countries from going down the dangerous reprocessing road, including a continued embargo on the export of certain equipment and technology.

But some of the old vigor and some of the critical parts of the position were missing. In a campaign speech in San Diego last September, Mr. Carter said that, if elected, he would condition new commitments to sell nuclear fuel abroad on the willingness of those countries receiving it to forgo national reprocessing plants. Now it is not even certain that he will object if countries with such plants use them to reprocess nuclear fuel we sell them. Nor it is clear that he has much hope that the countries pursuing this technology can be persuaded to choose a better alternative.

In fact, Mr. Carter seemed unaccustomedly resigned to the idea of national reprocessing plants and even to agree that there is a "need" for them in certain places, speaking of "countries that have to reprocess nuclear fuel" and remarking that Germany, Japan, Britain and France "have a special need that we don't have in that supplies of petroleum products are not available." There is much in the rest of Mr. Carter's remarks that contradicts this fallacious notion of reprocessing as the inevitable and productive alternative to running out of oil, so that the position stated last week does not add up to a consistent whole. But it seems to us that what is most notable about it is Mr. Carter's new disposition simply to accept reprocessing as an unalterable fact of life in those countries that are already at some stage in the development of the technique.

So far as we have been able to find out, this new acceptance, came about after our various reprocessing allies raised a lot of hell about an earlier, tougher version of the Carter position, which they had been shown. This evidently occured in the middle of the SALT mission ruckus, and Mr. Carter backed down. The purpose of his having done so is now said to have been to get the French, Germans, et al., to cooperate in some sort of international "evaluation" program, which they evidently refused to do unless the American position were softened - which it was. The question is whether the President, having begun his term with some fairly heavy-handed attempts to get other countries to call off the sale of reprocessing equipment abroad, has not now leaned over much too far in the other direction. Mr. Carter's courtly and "understanding" statements are said to have made it possible for those countries now working on the reprocessing technology to come to the table to discuss with him the problem of plutonium. We wonder. Those statements went so far in seeming to validate the "need" for this technology that some of the most important questions to be discussed may have been mooted.