The arguments now swirling round President Reagan's proposal for 100 MX missiles to be bunched together near Cheyenne, Wyo., ought to be broken down into two parts and each one argued separately.
First there is the question of whether the US really needs another weapons system for its nuclear deterrent.
The second, and entirely different, question is whether the MX is the best and least expensive way of getting what is presumed to be needed and wanted.
The President spent most of his time in his dramatic radio speech last week arguing for a new weapons system. It was a fine piece of theater. There was hardly a dry eye in the house when he talked about ''our boys'' having to fly planes built before they were born. He made it sound as though the Russians were about to overwhelm the world tomorrow with their alleged superiority.
You can safely forget most of that for two reasons.
Mr. Reagan's tables of statistics were carefully selected to make the Soviets look 20-feet tall and America's arsenal pitiably weak.
He omitted the fact that one new system, the fitting of nuclear warheads to unmanned planes called ''cruise missiles'' is almost ready for deployment. Three thousand have been ordered. They can be launched from air, sea, or land. The maligned old bombers are being refitted to carry cruise missiles. The missiles can be launched safely from outside enemy territory and reach their targets on their own devices. The first squadron of B-52s fitted with cruise missiles should be in the air by the end of the year.
One B-52 bomber can carry 12 cruise missiles.
He omitted the fact that 33 US missile-carrying submarines, now including the first three of the new Trident class vessels, can keep station two-thirds of the time and can avoid Soviet detection. Soviet submarines are on station only half the time and are detected and followed by NATO surface ships. This is estimated to give the US an advantage in submarine-launched warheads sufficient to balance off the present Soviet advantage in land-launched missiles.
He omitted the warheads which US strategic bombers can now carry (pre-cruise missile phase). The President's charts showed the Soviets with a total of 7,500 warheads against 7,100 for the US. The International Institute for Strategic Studies counts the bomber missiles and shows the US with a total of 9,268 warheads against 7,300 for the Soviets.
So, America is not so far behind. We must hope that Soviet intelligence is good enough for Moscow to know this and so ignore Mr. Reagan's tables. If they believed them they might do something dangerous. The more serious danger is that some ally might believe them, take fright, and run.
The other reason why the incomplete tables don't really matter is that Congress is virtually certain to give the Pentagon something new to do what the MX is specially designed to do. It is designed to deliver high accuracy and heavy yield warheads.
The race in nuclear weapons is now in accuracy and yield. The Soviets have one launcher, the SS19, which is credited with being able to come within 300 feet of its target half the time. It can lift either six 550-kiloton yield warheads or a single one of five megatons (the equivalent of 5 million tons of TNT).
The MX is supposed to be able to equal the accuracy of the SS19 - coming within 300 feet of target half the time. It could be fitted with warheads in the megaton range if desired. The yield of the warhead can determine the number which can be fitted on a particular missile.
The latest Minuteman III is supposed to have an accuracy now of 220 feet. But it cannot throw as many warheads with as high a yield as the MX can. The latest model Trident missile is credited with an accuracy of 450 feet. It carries eight warheads of 100-kiloton yield - not enough to satisfy the Pentagon desire for higher yields and more accuracy.
But the next generation of Trident missiles is supposed to be able to reach the same accuracy as Minuteman. They could be designed for fewer, but higher yield warheads. More Tridents could be built to take over more of the deterrent load from Minuteman which is supposed to be too vulnerable now to the newly accurate and powerful Soviet missiles.
And cruise missiles, much cheaper to build than Tridents or MXs, could be fitted with accurate and higher-yield warheads.
The real argument is over whether to keep a land-based deterrent, which is deemed increasingly vulnerable, or forget about land basing and put the deterrent into various mobile forms. The cruise missile can take over from manned bombers when and if they become obsolete. It can be land launched from a mobile vehicle. It can be launched from the seas - from surface or undersea. The MX is not the only possible answer to the Pentagon's problem.