For several weeks now, we have been treated to no end of exciting and/or terrifying news reports of a presidential directive dictating a new "limited nuclear war" strategy. In the U.S. choice of Soviet targets, "official sources" have breathlessly confided, there will now be a distinct switch away from population centers in favor of military installations and political command posts.

Anonymous authorities have advertised a whole new concept -- a new readiness on the part of defense planners actually to fight, rather than to try to deter, a nuclear war.

The background briefers' reward has been a big press play.

But when Secretary of Defense Harold Brown set out last Sunday on a network news show, ABC's "Issues and Answers," to provide the first official explanation of what was going on, he might as well have tucked it away in the Federal Register. And never mind that the "new nuclear war strategy" by his account turns out to be not particularly new, and still less a "war" strategy.

Asked specifically if the Carter administration has embraced "a new concept of limited [nuclear] war," Brown replied:

"The chance is an evolutionary one. It has always been the policy since the 1960s . . . in retaliating to a nuclear strike that the United States would not only hit urban industrial targets, not only cities, but also military targets. That's not changed now.

"[But] in recent years, two things have happened that have caused us to reexamine the strategy -- the details of the strategy -- and carry this evolution one step further.

"One is that the Soviet Union has greatly increased its nuclear capabilities. . . . There has also been some indication that at least some of their people think a nuclear war might be winnable. . . . We don't believe it, and it would be very dangerous if they did. So we have felt that it is important to give the president more options. . . .

"But again, I must emphasize that this is not a revolutionary change in doctrine. . . . We believe in deterrence, our approach is retaliation, and what we are talking about is the detailed nature of that retaliation."

Is Brown, on the record, somehow less noteworthy than the background briefers? That's part of it. Not-for-attribution briefings by responsible officials are often (and sometimes rightly) given a higher authenticity rating than carefully prepared, guarded public statements. But there is something else you should bear in mind about calculated leaks: they tend to flourish, and catch attention, in every administration in direct proportion to the level of dissent and disarray -- and in inverse proportion to the level of loyalty and leadership.

And that, to my mind, is what's immediately important about this whole affair. It's a close question, on the merits, whether "more nuclear options" means more deterrence. Precisely what combination of American nuclear capabilities would give the Kremlin pause is hard to know, and still harder for outsiders to second-guess.

But there is no close question about what this performance adds to the general impression (already severely damaging to the Carter presidency and the Carter candidacy) of mismanagement. Brown's explanation is, at least, cogent. If it had been the first word, it might even have been very nearly the last; the argument on the merits might have run on, but there would have been a lot less in the substance of the matter to argue about.

There are several suppositions about why it was handled the way it was -- all of them shabby. One is that Secretary Brown was supposed to have explained everything in a public speech, but not until after the Democratic convention, so as not to unsettle the delegates -- and then it just slipped out. That's the government-out-of-control theory.

Another theory is that this was an effort, to which President Carter himself was a party, to give a fast answer to the Reagan/Republican line at the Detroit convention that the administration is indifferent to a growing Soviet nuclear threat. A third theory, not inconsistent with the second, is that the leaking was yet another round in the internecine struggle between the president's national security adviser, Zbigniew Brzezinski, and the Department of State -- a thumb in the eye to Secretary Muskie, who has made a big fuss about not being consulted.

You can take your pick -- none of the theories does any credit to the president's capacity to command. As of this writing, two weeks after the fact, Jimmy Carter has yet to express a public, presidential interest in a matter of self-evident presidential concern. That's the same Jimmy Carter who, in a convention platform fight over the MX missile, traded on his title as commander of chief in a personal, handwritten note to every delegate.