In the car the other day, my son started to talk about nuclear war. He thinks it's a possibility, and since he is young and does not want to die young he considers nuclear war "unfair." It is his favorite word, but there is for the moment, none better.

He is not the only one talking about nuclear warfare these days. The subject is suddenly in the air. The New Yorker, which can guarantee an article obscurity simply by publishing it, ran a three-part series on nuclear war last month by Jonathan Schell and people are still talking about it. Esquire did one on civil defense and now Time has the bomb on its cover.

In New England, town meetings dealt with the issue of nuclear disarmament, and at dinner the other night an economist I know kept punctuating his explanation of which way the economy was going by saying, "But that's if there's no war." And that same week, my wife had lunch with a well-known political consultant and reported that he, too, was talking about war.

Suddenly, war seems a lot closer. It seems that the whole country has turned 40 and death that was only theoretical at 39 seems now to be imminent. Those of us with a memory have been through this before. The late 1940s were rough and the '50s were no fun, either. We learned how to take cover under schoolroom desks and we were marched into the hallway and told which way to face. We were told never to look into the blast and to cover the backs of our necks and to listen to our teachers. It was silly but after a while it all went away.

Now it is back and the reason is that the Cold War is back, too. Ronald Reagan and Alexander Haig and Caspar Weinberger, with their talk of limited nuclear war and firing nuclear warning shots, their tough rhetoric and their incessant military posturing, have given the whole country the willies. They seem to have doused hope, made you wonder why you thought in the first place that things were getting better -- that nuclear war could not happen.

They are the hard guys, the realists. They talk blithely of bombs and war because bombs and war are always a possibility. They want us to face facts, but the facts they want us to face are truly horrible. There are now about 50,000 nuclear warheads in the world -- Hiroshima and Hiroshima and Hiroshima over and over again until you get to 50,000. Only the Hiroshima bomb, 12.5 kilotons, was a puny affair. Still, it leveled the city, killing half the people in it. Nowadays, Jonathan Schell writes, "it would be classed among the merely tactical weapons."

For most of us, nuclear war, like one's own death, is unthinkable, and so we have left the thinking of it to others. But what is refreshing about what is happening now is the apparent refusal of lots of people to accept nuclear war as one accepts the inevitability of death itself. These are people who now are saying that something can be done, that the fate of the world is in the hands of the people of the world. This was the message of the antinuclear rallies in Western Europe. They weren't so much anti-American as prohope -- a statement by the people of Europe that they were no longer going to leave nuclear policy to the professionals. It was their lives, therefore their business.

Now the same thing is happening here. Only instead of the administration seeing that we are all on the same side -- that when it comes to the nuclear issue, there is no other side -- it senses a fifth column, a softness, a break in our resolve on which the Russians will capitalize. They fear the Russians will sense that we are afraid of nuclear war. The trouble is, this cannot be news to them.

So the drumbeat of belligerence continues. As a nation, we have our dukes up. Our missiles are on the move. Our defense budget will grow. We are no longer the 90-pound weakling of the Jimmy Carter era, but a broad-shouldered country, seeking to show that no nation can kick sand in our face.

All this has revived and exacerbated fears about Ronald Reagan that came out during the presidential campaign. Now, suddenly, little kids talk of nuclear war in their own way and lawyers in theirs. Mothers organize and the New England towns meet and the reason is that something has gone dreadfully wrong. Ronald Reagan set out to scare the Russians, but he's scared us instead.