Ronald Reagan says that if Congress doesn't buy the MX he might as well call his negotiators home from Geneva, since all he'll have left to put to the Kremlin is "talk." It is a barb aimed especially at those who say he has his foot too much on the arms accelerator and not enough on the arms-control brake. It is serious.

Let us concede right off that Reagan has some part of a point. There is a mindless element among his critics, and it denies that there is any threat, that any new arms are needed or that the Soviets need any incentive to negotiate a fair arms control agreement. This is no straw man: plenty of Americans hold views like these, and the freeze movement has brought them out in full force. It is not silly of Reagan to want to keep things in hand.

There is, furthermore, the Soviets' immediate reaction to his MX decision. They screamed bloody murder, saying, accurately, that the MX is a heck of a threat and suggesting, falsely, that they had no similar "first-strike" weapon; their SS18 is a silokiller like the MX. Their protests are sweet music to that school of arms control holding that the Soviets are only going to yield on the weapons systems that trouble us if we work on systems that trouble them.

To be sure, it is often asserted that Moscow does not bend to "pressure." An attempt to use a weapon as a "bargaining chip," this argument runs, will merely provoke the Soviets to match it and will leave the United States no better off in the end.

But the available record is inconclusive on this score. Our move toward building an anti-ballistic missile system helped bring the ABM agreement. Our moves to build other systems had no similar effect. Personally, I find it silly to ascribe to the Soviets some quality of bullheadedness, pride and paranoia that renders them unable to discern their interest. When they feel it's important, they'll keep stride with us or stride ahead, and when they feel it's not, they won't.

There is a bit of turbulence inside the administration over whether the MX is a "bargaining chip," to be traded off at Geneva, or a "bargaining lever" or "bargaining issue," to be used to pry out Soviet concessions for which the United States would pay in other strategic coin. The former was stated by a White House spokesman, but what one hears elsewhere is either that the MX is too valuable to trade or that its fate will depend on how things go, on what the Soviets might pay for it.

There's a contradiction here arising from the dispute over whether the MX will actually work: the more you say it will work just fine, the more you will be tempted to ask for it in a negotiation; the more you say it's a lemon, the less you can ask for it. The one way to escape this contradiction is for our negotiators -- our president -- to use good judgment at the table.

As it happens, this is the area where Reagan is perhaps most suspect, and it raises a question his critics haven't even gotten to yet. Do you make him bargain more your way by taking a card out of his hand or would that make him hang all the tougher?

I pass. Perhaps it's enough to say now that no one should pretend striking down the MX will make no difference. Meanwhile, there are other considerations.

First, it defies public decency to build a weapon to bargain away that you don't think makes adequate sense to build and keep. (That's one reason why many officials did not want to publicly label the MX as a "bargaining chip" -- read $26 billion throwaway -- in a tight-budget year.)

That doesn't mean no weapon can be removed from the board once built: if the price is right, sell. It means that no weapon should be built that does not have a true value. The political community appears very divided -- the division itself is an embarrassment -- on whether the MX meets that test.

Nor need the president contend that if the MX is shelved, his negotiators will have a bare hand.The United States is already building, over no political opposition to speak of, new subs with new missiles, new bombers and new bomber missiles, new land-based missiles (ballistic and cruise) and so on -- more than enough to still the anxieties of all but the most fearful among us.

The president risks undervaluing his remaining Geneva hand by ignoring the other American forces being modernized and by assigning an inordinate weight to the one weapon in political jeopardy at home.