The first of the postwar commercial films on Vietnam opened here the other day. It is a good movie, but it is not (or maybe because it is not) about Vietnam.

It describes a damaging national disease that afflicts a lot more Americans than were ever touched by the war. Well-nigh unconsciously, it offers as a cure what amounts to this country's favorite illusion.

"Heroes," as the film is called, tells the story of a Vietnam veteran who escapes from the mental ward at Bellevue and makes his way by bus and auto across the country to Eureka, Calif. His quest is for three buddies who had agreed during the war that afterward they would set up a worm farm.

The first of the buddies has gone back to the family farm in the Midwest. But his parents have left, and he doesn't get on very well with his grandparents. He lives by himself in a trailer.

Nor does he like farming all that much. He has bought himself a souped-up red sports car, which he plans to enter in local automobile races. "It's just round and round and round," he says of life.

The second buddy never appears. His wife, a middle-class black living in a comfortable home, explains that he has left her, and has been doing it on and off ever since the war. "He drifts," she says.

The third buddy turns out to have been killed in the war. His parents don't want to have anything to do with their son's friend. Rejection causes the friend to hallucinate all the horrors of the war, and he starts to come apart.

He is saved from madness by two characters. He himself is one. The hero of "Heroes," the veteran in quest of his buddies, is played by Henry Winkler, the remarkable comic who is the Fonz in the television series "Happy Days." In "Heroes," Winkler is the Fonz all over again - a decent, relaxed kid who means very well, likes people and has no intellectual acumen, skill or even training. Because he has a "good attitude" toward life, he is able to foil various baddies in the movie: a bus driver, a pretentious psychiatrist and several sets of cops.

He is also able to pick up on the bus a delightful young woman. The young woman was supposed to have married a man in New York. Though he does not appear in the film, he is made to seem like Mr. Gottafuture. Just before the marriage she drifts off on a bus trip to discover herself.

She meets the touring veteran and, turning her back on marriage, joins in the search for the buddies. At the end, he avoids madness, because she takes him in her arms and assures him that he's alive and well and has nothing to fear.

That bare narrative conveys none of the charm of the film. But it should bring out two points that underlie the film and make it a true, even important, reflection of the way we live now.

First there is, on the part of the young people in the movie as in life, an unholy terror of the established way of life as a responsible adult. They don't have jobs. They don't get married. They don't belong.

The people who do fit are all representated as unattractive and unfeeling. The psychiatrists and unfeeling. The psychiatrists and the various cops, for example, are bureaucratic robots going through prescribed motions that have nothing to do with the welfare of the young veteran for whom they are supposed to care.

Second, there is the recommended formula, for dealing with the horrible, cold, unfeeling and corrupt outside world. It consists of going limp, of not being uptight, of having a good attitude. Hard work, training, even thinking are for the birds.

One movie, of course, does not make the spirit of the age. But my instinct tells me that the America I have been seeing at many levels and in many parts of the country over the past few years is the America of "Heroes." It is a country full of individuals who entertain such dire suspicions of established life that the only thing they are into is themselves.