Remember "Suppose they gave a war and nobody came"? Well, I've got a friend whose thoughts are running the other way: Suppose they achieved a peace and nobody noticed.

Here we are on the brink of signing a major arms-reduction agreement with the Soviet Union, a treaty that negotiators on both sides profess to see as a first step toward a nuclear-free world, and nobody seems to be paying very much attention.

My friend is flabbergasted. He knows that there are problems with the proposed treaty. He knows that there is reason to doubt the worth of Soviet pledges (just this week, the Reagan administration accused the Soviet Union of new technical violations of the 1972 Antiballistic Missile Treaty). And he knows that the treaty to be signed next week will fall far short of insurance against nuclear disaster.

Still, he insists: "The significance of what is about to happen is not the number of warheads that will be dismantled, or that the threat is about to be eliminated. The significance is the reversal of a trend. The march toward nuclear holocaust, which had been the overriding issue of our age, is being reversed. That strikes me as momentous."

But while next week's summit is very much in the news, and everybody expects Reagan and Gorbachev to put their names to a treaty eliminating medium- and shorter-range missiles, there is, in the public discourse, no sense of breakthrough, no feeling of having turned away from the brink, no "Hallelujah" that we are about to take a tiny step toward nuclear sanity.

What we get is muted support from the left and technical objections from the right.

"I don't understand it," my friend says. "Is it because there has been so much discounting in advance of the treaty, so much emphasis on what won't be included? Is it because we have grown skeptical -- even cynical -- on the question of peace? Is it because Reagan is a Republican? I don't know."

I don't know either, but I share my friend's consternation. It seems such a short time ago that we were agonizing over "The Fate of the Earth" and "The Day After." Only yesterday, it seems, we were reading about schoolchildren so overwhelmed with nu-clear fear that they were having nightmares and seeing psychiatrists. We had almost stopped believing in the possibility of nuclear disarmament.

It has been a lot of years since we stocked apartment-house basements with emergency rations or argued the ethics of keeping neighbors out of our limited-space fallout shelters. But we still debate evacuation routes and hardened silos and the maintenance of retaliatory capability as though nuclear war is a real possibility.

If we still believe the possibility, why aren't we elated at the move to reduce the number of nuclear warheads? Why aren't more of us sharing my friend's feeling that next week's signing will mark the closing of a dangerous cycle?

"Everybody's talking about the newly urgent need for conventional sufficiency, the notion that mutual reduction in nuclear capacity might well increase the likelihood of people dying in conventional war. It's all true. Solutions always create new problems. But these new questions are signs of success, as nuclear war recedes as our overriding concern.

"I mean, I ask myself which is the larger problem. Is it the increasein the likelihood of conventional war (or the fact that nuclear capacity of some small countries like Pakistan won't be affected by the treaty)? Or is it the prospect of all-out nuclear war, which this treaty will render less likely?

"The nuclear threat seems the more significant problem. It's what we've talked about for a generation, what we worked so long to reverse. And now Reagan and Gorbachev go on TV and talk about it, and, come Tuesday, they'll sit down and sign a treaty. That's a dramatic step forward."

He acknowledges that the treaty could, conceivably, turn out to make very little difference, that it might be chock-full of loopholes, or that it might be overtaken by technology.

"But this is something people have been hoping for for 35 years," he says. "Now that we've got it, I in-tend to spend the next month enjoying it."