PRESIDENTIAL directives dealing with nuclear strategy can have a value in forcing the people who are responsible for these things to finish their sentences and face up to the implications of their policy. But there are also several respects in which these documents are endemically and incorrigibly phony.

First, no nuclear war could conceivably bear any resemblance to the scenarios assumed by these statements of strategic intent: if they do this, we do that, then if they come back with this, we can do the other . . . and so on. Invariably, bloody nuclear chaos is made to sound like something taking place on the center court at Wimbledon.

Second, the best people in our strategy-making apparatus know this. And their acknowledged purpose is not to lay out a prospectus for real war, but to create possibilities of action that, once known and believed, will discourage an opponent from trying us or from pushing too hard. So, it is perceptions of reality, not reality itself, the Pentagon planners are mainly concerned with. Defense Secretary Harold Brown said as much in his Annapolis speech Wednesday.

Finally, merely as an exercise in policy-setting these documents have a certain air of fraudulence to them. It's not always so certain (and the present case is a good example) that the strategy preceded the weapons development needed to fulfill it. The strategy can be an after-the-fact justification or a belated acknowledgment that, whatever we were claiming our strategy and intent to be, we were, all along, developing an arsenal that could and would do something else.

There is a pronounced element of this post facto reasoning to the announcement that we have now formulated a nuclear strategy vis-a-vis the Soviet Union that incorporates the improved accuracies and other changed characteristics of nuclear weapons under development. For a long time, American government spokesmen were more or less forswearing certain war plans for which the government was, however, simultaneously beginning to create a uniquely suitable arsenal. And there have also been official statements and hints and lurches and lunges along the way to revelation of PD59 that such a change of strategy was being fashioned. When Secretary Brown said this was nothing new and not a total policy reversal, but something evolved and partial, he was no doubt absolutely right. And it also seems reasonable to us that there should have been some evolution. Much in the alternative scheme that this one supersedes had taken on the attributes of an immutable, sacred doctrine that it was heretical and bloody-minded even to question, no matter how politely or from what responsible motives. Nor did that alternative evidently make sufficient provision for dramatic changes in Soviet planning and strength.

But having acknowledged all that, we are bound to say there is something plenty fishy about the manner of disclosure of the altered strategy and the exclusion of Secretary Muskie from knowledge of what was about to happen. It cannot have been inadvertent or merely "thoughtless" or justified by any theoretical division of labor and jurisdiction: it was a calculated freeze-out. Mr. Muskie was thereby denied an opportunity to argue or discuss or recommend anything in relation to a presidential decision concerning the topmost order of national security business, a decision bound to have seismic reverberations in his own field of activity. He was faced with an accomplished fact.

Secretary Muskie was right to be furious and noisily so. Is he there for window-dressing? Is he going to be cut out of the big game when it involves that supremely important interconnection of military, strategic and diplomatic concerns that actually defines the U.S.-Soviet relationship? There is a downside to the evolutionary trend that has led to PD59, and you get the idea from what happened to Mr. Muskie that someone, somewhere might have been afraid that he would make that negative argument, that resistance, real or imagined, was being preempted.

If this is so it doesn't say much for the way in which the final decision was reached and inevitably -- fairly or not -- raises questions about the decision itself. But the alternative hypotheses aren't better. Did someone -- everyone -- "forget" the secretary of state's claim to concern in these matters? Was someone trying merely to upstage and overwhelm him on the bureaucratic battlefield? For whom was the leak of the change of strategy intended? The Russians? The Republicans? The voters, bless their poor, much put-upon souls?

An administration under attack politically for a sogginess of spirit and weakness of will in defense matters surely has the right, even the duty, to answer back. And it also has the right/duty to let the potential aggressor whom all this hardware and planning is meant to deter from aggression know what American intentions are. But no administration serves itself or its constituency or the credibility of its policy when it lets disorderly and self-aggrandizing and suspicion-breeding politics get into the act, and is seen to close a key player out of the argument. That unfortunately is what seems to have happened in the PD59 affair.