THE EXTRAORDINARY thing about the MX debate is that in the fifth year of an administration which won reelection on a platform of military strength, the particular weapon most symbolic of that quest for strength remains in deep political trouble, no matter that it cleared one hurdle in the Senate yesterday. We continue to think that Congress should approve release of funds to produce the second 21 of these missiles: What the MX may not do for strategic stability it may do for bargaining advantage. But no matter how the votes finally come out, the president's struggle to get them tells a political tale.

Is there left a legislator who has not received a personal MX appeal from President Reagan? The scale of his exertion falls somewhere between formidable and epic. Perhaps inadvertently, he has set a new standard of presidential commitment against which his subsequent appeals for this or that are bound to be measured. Yet his appeal has been resisted, if not altogether rebuffed, not merely by legislators of a different partisan or ideological persuasion but also by defense-minded legislators, including some in his own party.

The upshot is that even a victory in the current series of votes will have a Pyrrhic quality. It cannot possibly produce the success at Geneva that many people will have been led to expect by the president's dire warnings of what a negative vote would bring. His campaign has taken important swing legislators to a point where they may reluctantly support MX now, chiefly because of the damage a no might do to the American position at the Geneva talks, but they are darned if they will vote for the 48 additional MX missiles needed to complete the administration's MX buy. Meanwhile, the MX has become a leading exhibit in the general indictment holding that the Reagan administration throws money at military problems without knowing what it is doing. This indictment, key defense legislators believe, is bound to make its mark on the administration's defense planning and spending across the board.

It is unfair to put the entire burden of the MX on the Reagan administration: the missile was, first, a Ford and Carter project. But Mr. Reagan did not merely inherit an arguable missile program; all missile programs are arguable. He also added a philosophy -- build great strength and negotiate from it -- that does not lend itself easily to the proportion and intelligence that even many of his supporters feel ought to be essential elements in American security policy. Proportion and intelligence: these are, after all, the quintessential conservative virtues. The MX without "Star Wars" was one thing; the MX with "Star Wars" is . . . well, people want to think about it. The president's seeming indifference to a proper connection between defense and the deficit adds to concern.

Is there in the Reagan administration an awareness of the range and depth of reservations it has stirred on security issues, among its friends as well as among its political adversaries? It does not bode well that, regarding the MX, the president felt it necessary to launch a Normandy invasion to capture such a relatively small objective. What Mr. Reagan most needs to demonstrate, and most of all to the Russians, is a command of the American political arena. And yet that seems to be where his frailty lies.