When it comes to the debate over defense expenditures, I'm feeling more and more like a slow pupil late to class. I hear what the teacher is saying; I hear the arguments among my fellow students; I perceive, at least dimly, the statistics they toss about. But none of it makes sense to me.

Well, some of it does. I have no trouble with calls for money for spare parts for existing weapons, especially the tactical stuff that we seem reasonably likely to use. I understand the call for improved pay and other means of attracting and keeping military personnel. I accept the general necessity for military preparedness.

It's the big picture that keeps going fuzzy on me. The implication of the arguments for massive new defense outlays (particularly the outlays for such major new weapons systems as the MX) is that if the Soviets ever get ahead of us in strategic capability, they will attack us, or at any rate blackmail us with the threat of attack.

But two things confuse me. First, I don't understand what it means to be ahead in this madness if both we and the Soviets already are capable of destroying each other several times over. I've had it drilled into me that we've got enough sophisticated early-warning systems that we can spot their missiles long before they arrive here and, therefore, will have plenty of time to fire our own missiles at them.

The result of such an exchange would be the devastation of both the Soviet Union and the United States. And if that is so, what conceivable difference would it make if either of us had the capability for a second, or sixth, or 100th fusillade of missiles?

Second, if our supposition is that the Soviets will attack (or blackmail) us if they ever get ahead in the arms race, what does it mean that they haven't attacked? Doesn't it mean either that our supposition is wrong, in which case the whole argument falls apart, or that they are not in fact ahead, in which case there's no necessity for catching up?

Okay, maybe we're not behind yet, but won't we fall behind if we just sit still? I don't understand that one either. If it is logical for us to keep spending ourselves silly to keep ahead of the Russians, isn't it logical for them to do the same thing to keep ahead of us? Wherein is the enhanced safety for either of us?

Isn't there at least as much safety--and in all probability a good deal more--in a mutual reduction in our military outlays? So why are we paying so much attention to where we will deploy our MX missiles (whose chief function is to replace our now-threatened Minuteman missiles until the Soviets come up with a credible threat to the MX, at which time we'll have to develop and deploy to replace that) and so little attention to SALT?

There's another thing I don't understand. Why is Western Europe, which would seem to be a more inviting target than the United States, so much less exercised over the Soviet threat than we are? Is it because the Europeans are pacificist chickens, or is it because they are too smart to play our silly game?

I don't want to come off as hopelessly naive, so I won't question the assumption that the Russians would attack us if they thought they could get away with it. But it does strike me as indisputable that they can't get away with it, and that they know it. Both sides have long since achieved what used to be described as the balance of terror or "mutually assured destruction" MAD for short. If the only thing staying the Russians is their certain knowledge that to attack us would assure their own destruction, what do we buy with massive new expenditures? If the price of destroying us is their own annihilation, what is the point of counting missiles and warheads and throw-weights?

None of these questions seems to be anywhere in the lesson plan, and because they aren't, the questions that are there don't make sense to me.

Maybe they aren't supposed to. In some ways, it's like the endless debate over gun control, where facts routinely take second place to emotions, to gut feelings.

My own gut feeling is that I am far more threatened by the domestic consequences, in slashed social programs, in inflation and in soaring interest rates, of our runaway military budget than I am by the Soviets' baleful intentions. It may be true that our mutual madness has bought us both a modicum of security, but it does not strike me that more madness means more security.

One more thing: if we see the Soviets as military madmen, committed to wiping us out as soon as they sense the slightest advantage, why the hell are we selling them wheat?