I can't wait for the moment at Geneva when we are told the American negotiator pushed 21 missiles across the table and said to his Soviet opposite number, "Okay, it's a deal." Then the Reagan administration would tell us exactly what pieces of Soviet nuclear hardware slid over to our side of the table in return.

It won't happen, of course. The administration's belabored "bargaining chip" argument in last week's MX debate made only slightly more sense than the case for an immediate signal of "strength" to the Soviet Union in response to the murder of an American officer by a Soviet sentry in East Germany. The House wasn't voting on whether to take anything away from the negotiating table; it was voting on whether to add something -- a move that the Soviets can match in an equally pointed way if they feel the need.

Leaving that aside, the administration would have been better off hustling these 21 more MXs on their merits. If they're worth the cost ($1.5 billion) the case should be made in terms of the existing balance of U.S. and Soviet forces and the almost certain prospect that nothing is going to happen in Geneva to alter that balance any time in the foreseeable future.

Arguing it the administration's way may have carried the day. But it should also leave sensible and responsible Democrats with a relieved sense of having stepped off a curb and been narrowly missed by a bus. For it leaves the Reagan administration with no one to blame but itself (or the Soviets) when the excitement of Geneva's first days inevitably wears off and the long, mind-bending, nitty-gritty bargaining begins -- with nothing to show anytime soon for that supposedly fateful "bargaining chip."

Soon enough, it will become apparent that all that trashing and bashing and tender, loving attention to the local political needs of the anguished congressional waverers -- not to mention the lobbying by chief arms negotiator Max Kampelman, the president, and the secretaries of state and defense -- blew MX all out of proportion to its likely bearing on the arms talks. In the process, it also blew the arms talks out of all proportion to their true prospects for altering the course of U.S.-Soviet relations or substantially restraining the arms race in the months or even years ahead.

Soon enough, the administration is also likely to discover that, by making such a big deal out of such a relatively small deal, it may not only have done the Democrats a favor but set itself up for a fall.

That's not to say that the Soviets are unimpressed by demonstrations of American resolve -- by the "signals" we send and by how they are received. They are. That's precisely why the MX super-hype is a dangerously shortsighted piece of sophistry. The Geneva nuclear arms talks are just about all that there is to U.S.-Soviet relations these days.

This makes it all the more important that they be handled with care. They constitute almost the only measure of the intentions and attitudes of the two superpowers whenever their conflicting interests threaten confrontation around the world.

Having made last week's MX vote so vital a test of "America's strength," what will the Soviets make of the next MX test lying ahead only a few months from now? To fill out its MX inventory, the administration is committed to ask Congress for 48 more MX missiles (cost: $4 billion) later this year.

If, by that time, Geneva is as unproductive as most experts predict it will be, will the "bargaining chip" argument be trotted out again? More to the point, will it have the same effect?

Apparently not, according to reports from Capitol Hill. Already, the House Democratic whip, Thomas S. Foley, is ready to statthat the next batch of MX missiles is "in serious trouble." The Republican House leader, Robert Michel, seems almost to be saying that last week's MX supporters might be justified in taking a harder look at the proposition the next time around.

A good many Democratic defectors from their party's leadership in the House are also making it clear that in exchange for their support for the 21 MX missiles, they will not only feel free to take a different view on the rest of the MXs. They will be compelled to press all the harder for deeper cuts in the defense budget across the board by way of demonstrating their devotion to economy.

What all this suggests, then, is that the administration focused on the tactics of the moment at the expense of any long-haul strategy.

The price for last week's show of strength may be a far more significant signal of weakness later on -- assuming the Soviets take these "signals" as seriously as the administration would have had Congress believe last week.