IN COUNTRY by Bobbie Ann Mason (Harper & Row: 245 pp.)

We will remember Sam, a 17-year-old girl from Hopewell, Ky., who watches Johnny Carson, listens to old Beatles’ records and whose pride and joy is her secondhand Volkswagen.

In Bobbie Ann Mason’s novel, “In Country,” Sam stretches the imagination of our times. Ten years after the end of the Vietnam War, in the most prosaic and magical way possible, she stubbornly undertakes the exorcism of a ghost that almost everything in our everyday life manages to bury.

Mason is the author of “Shiloh,” a collection of short stories in which the dehumanizing accouterments of contemporary America--which precipitate an Ann Beattie or Frederick Barthelme into a frozen value-state--serve quite remarkably as the implements of believable human passions. “In Country,” a brilliant and moving work, uses them to furnish a moral tale that entwines public history with private anguish.

One of the questions for post-war American literature, dealt with variously by Updike, Cheever, Roth, Salinger and a host of others, is whether the larger capacities of the human spirit can be exercised, so to speak, in a motel room equipped with color TV and a drinks refrigerator. The answers vary; Mason has found her own striking variety of “yes.”

Sam’s father, whom she doesn’t remember, was killed in Vietnam. Her mother has remarried and moved to Lexington. She and Sam are close, but Sam chooses to stay in Hopewell for her last high school year; partly because her boyfriend is there; but mostly to keep her eye on Emmett, her uncle.

Emmett was also in Vietnam. Since his return he has drifted, bird watching and taking care of the house. He lacks focus; unable to keep a job or a girlfriend. His health is uncertain; he gets stabbing headaches and acne that won’t go away.

There is a touch of exaltation to Sam and Emmett; a sensitivity and a closeness that may recall something of Salinger’s Glass family. Perhaps that prepares us when, despite Sam’s resolute teen-age normality, her uncle’s uncertain health makes a visionary out of her.

Listening to the news reports reading an article here and there, through chance conversations, Sam becomes convinced that Emmett is suffering from the effects of Agent Orange. His pimples and pains become a sign of the times, like Camus’ plague. They set Sam off on a remarkable quest whose object is to relive the Vietnam War that has taken her father, sickened her uncle and that seems to her to infest the life around her, even though nobody else wants to notice.

“Don’t fret about this Vietnam thing, Sam,” her mother advises her. “You shouldn’t feel bad about any of it. It had nothing to do with you.” And Emmett doesn’t want to talk about it. But with nothing fey or winsome about her, and despite her charm and occasional vulnerability, Sam proceeds to make a determined pest of herself. It is no abstract sense of mission. Mason has provided a perfectly concrete goad. It may be the American thing to forget about the past’s unpleasantness; but it also the American thing to worry about bad skin.

Sam sends away for State Department documents. She reads “books without pictures” about Vietnam. She grills other Vietnam veterans in town, pressing them to tell her what it was like. She tracks down stories about Agent Orange symptoms.

More important, she searches the trivia of everyday life for images of the past it ignores. She and Emmett religiously watch old MASH reruns; she studies them for what they may suggest about Vietnam. The death of Col. Blake gives her, for a while, a way to think about her father’s death.

Emmett smokes while filling the gas tank, and she visualizes ammunition dumps exploding. Attracted to one of her uncle’s veteran friends, she follows him across the parking lot to his car, thinking of herself as a Marine following the man on point. Sodium lamps suggest the glare of napalm. To get the feeling of sleeping in the jungle, she takes a tent out to a nearby swamp where insect bombs constitute technological mass murder.

She hurls herself into her quest, by turns quixotic, comical and touching. And what she finds confuses her.

Her father’s diary and letters, which she pries out of her mother and grandparents, portray neither a hero nor an anguished victim, but simply a young man as normal and boring as the boyfriend she is in the process of discarding. Emmett, when he does talk, can express no more than the dimensions of his numbness. She sleeps with the veteran friend, only to find that he is impotent and that her empathy is perfectly useless.

Nothing dramatic happens; yet Sam’s pilgrimage takes on a mounting tension. And there is a sense of purgation when she, Emmett and her grandmother drive her battered Volkswagen to visit the Vietnam Memorial in Washington, D.C. It is a journey as ordinary as it can be--fast food, motels, a broken clutch--but it is also as grave and as merry as a children’s crusade.

The climax is beautifully told. All that occurs in the polished black canyon is the ritual searching of the names of the war dead. Yet Mason convinces us that something very important has taken place. That every bit of the popular culture we live in is poisoned by the ghosts it denies; and that by remembering them, we let in sanity and health.