ALL THINGS being equal, the president could make his decision concerning the procurement and deployment of neutron weapons in a clean, isolated, even philosophical way. He could weigh the military pluses and minuses of these so-called "enhanced radiation" warhead strictly in terms of whether they would - as some argue - 1) make East-West war less likely by providing NATO with relatively "clean" and controllable tactical nuclear weapons that an enemy would readily believe the Western forces might use or 2) - as the counterargument goes - make it all too likely that any East-West confrontation in the NATO area would turn into a nuclear exchange, since the very "manageability" of theneutron weapons would tempt the side that had them to introduce them.

But all things aren't equal, and that detached, clinical kind of choice is, in our view, no longer available to Mr. Carter - at least not without very bad consequences. We say this with more than routine reluctance and regret, because a year ago, when something more nearly akin to political and diplomatic lab conditions prevailed, we ourselves found it fairly easy to reach a judgment against the president's going forward with the weapons. We found the second of the views cited above the more persuasive. And we have held that opinion up to now. But it seems to us that the president has lost - in some measure, forfeited - the luxury of such a choice. We now feel that if neutron weapons are to be held out of the Western arsenal, they should be negotiated out with the Russians - and only for something considerable in return.

Let us be very plain about this: The most important altered circumstance that seems to us to argue for Mr. Carter's going ahead with a decision to procure the weapons is the evident unwillingness of the Soviet Union to slow even by a hair its buildup of what are called "theater weapons," a gigantic and ever-growing arsenal of medium-range nuclea missiles, tanks and the rest, trained remorselessly on Western Europe. American awareness of that buildup has become a good deal clearer and sharper in the last year or so.

The Soviets have also done much to transform the international politics of the issue into a circus. It is as poignant as it is preposterous that so many well-intentioned arms controllers have taken to the streets and Xeroxes to single out and protest this particular range of weapons. What is poignant is that the whole propaganda thrust of the Soviets - their effort to capitalize on the Western democracies' open internal disagreement on precisely this question - has altered the character of the decision Mr. Carter will make on it. It has made it more, not less, desirable for him to let the weapons go forward, at least to the procurement stage.

If the Soviets wish to influence the deployment of these weapons in the NATO theater they should be given every chance to do so - by the appropriate means, which is by trading off some of their own increasingly NATO-directed arms, arms that have had more than a little to do with justifying the need for the neutron weapons in the first place. We will be frank to say that Mr. Carter seems to us to have permitted the setting for his decision to get way out of hand and to have let the choice be framed by others for him. But now it seems to us he really needs to make a forthright, no-nonsense decision to proceed, with a view to negotiating the weapons out at whatever point in the production-deployment sequence an opportunity may arise to get a reasonable return.