IN CASE you don't keep up with these things, the latest Pentagon toy being developed by the U.S. Air Force is the MX, which is a method of moving Minutemen missiles through miles of underground tunnels so that the Soviets won't know where they are. We're talking about $30 or $40 billion if the Air Force gets to build the system, which the general in charge describes as being like a "shell game where you have one pea and three walnuts."

Nobody wants to fool the Soviets more than I do when it comes to pinpointing our missiles. But the cost of the project seems so great that I think we should seek out alternate ways of accomplishing the same thing.

At the moment the contracts for developing the "shell game" have been awarded to Boeing and the Martin Marietta companies. I believe the Air Force made a mistake in turning over the problem to them.

The company which should have gotten it is Amtrak, which runs most of the passenger railroads in the United States. The beauty of turning it over to the Amtrak people is that they already have the equipment and the know-how to fool anyone when it comes to figuring out where one of ther trains is at any given time.

Let us say you put a missile on an Amtrak train underground, in one of the tunnels. Then the Air Force puts out a schedule at which site the train will be, on that day, and at what time. They would make sure that the Soviets got a copy of the schedule as part of the SALT agreement.

Obviously the train would never be where the schedule said it would, and the Soviets would go nuts trying to figure out where the missile train was. It would accomplish the same goal as the MX program at half the cost.

If the Soviets protested that we were not living up to the SALT agreement, the Pentagon could invite them to send over their top generals and have them ride on an Amtrak train to prove the Air Force has no control over how the United States runs its railroads.

Once the Soviet command realizes that it could never depend on knowing where a missile train is going to be, it would be deterred from launching a first strike on our minutemen sites.

The advantage of the plan is that the money Amtrak received for this defense contract could be spent on new equipment and rails for its civilian passenger services above ground, and we would no longer have to subsidize this mode of transportation.

When I made this suggestion to an Air Force general, he had one major objection to it. "The trouble is that if we gave the contract to Amtrak, not only would the Soviets be fooled, but we ourselves would have no idea where the missiles were."

"I thought of that," I said. "What you could do is set up a hotline between Amtrak and Air Force Missile headquarters. It could be attached to a loudspeaker and an Amtrak announcer would man it 24 hours a day. He could say, 'Missile launcher 104 scheduled to arrive in Cheyenne, Wyo., at 11 a.m. will now be arriving on track 9 at 4 pm. this afternoon.' Or, 'Due to a derailment outside of Philadelphia, The Minuteman Limited, scheduled to leave tonight for Amarillo, Tex., has been canceled until further notice' or, Amtrak is sorry to announce that is Nuclear Comet, which was to stop in Baton Rouge, has been diverted to Denver because of inclement weather.' Amtrak would keep you up to date on every change in its schedule."

"It might work," the general said. "It certainly fits our one pea and three walnut strategy. The only thing that bothers me is that we've told Congress the MX system will cost $30 billion. If we now go back and say we only need $15 billion for it, the Air Force will lose all its credibility on the Hill."