Brian Evenson is a writer of disconcerting power. His stories are full of atrocity and violence. There is no human exchange in his work that is not steeped in brutality. An affluent young couple hurl kittens out of the window of their speeding car, laughing as the cats screech like power saws when they hit the pavement. An aimless drifter travels across America randomly slaughtering young women on whose warm bodies he then carves commemorative stars. A farmer stumbles on the body of his dead daughter, but rather than tell his wife he inexplicably buries the girl in an isolated barn.

All this could easily be dismissed as the work of yet another neurotic literary outsider, were it not for the fact that Evenson, 30, writes so well and that he is a high priest in the Mormon Church, a happily married father of two young daughters and an unequivocal believer. To him, the Book of Mormon is a text of sacred revelation.

A religious conservative, he will this week celebrate the 150th anniversary of the arrival of Brigham Young and the first Mormons in Salt Lake City. And yet, as Knopf, his New York publishers, acknowledge on the dustjacket of his collection of stories, Altmann’s Tongue , Evenson “appears, in every particular, to be the very destroyer of what he is instead the maker of”. In short, he imaginatively and, numerous critics say, gratuitously, violates what in daily life is most sacred to him: family life, faith and morality.

Not surprisingly, controversy has hit Evenson like a truck. He is reviled and scourged inside the Mormon community, where he is accused of putting himself on the side of evil. “There are people who wonder how somebody could speak in an evil person’s voice and not be affected by that voice,” he says.

If he continues writing fiction of experimental modernism, Evenson knows he will be excommunicated from the Church he has served in numerous roles. The prospect fills him with terror. For a fundamental tenet of Mormonism, one to which he is devoutly committed, is that marriage binds a couple to gether for eternity (polygamy, once rife among Mormons, has been outlawed for more than a century).

The only way they can part is if one of them is excommunicated. So Evenson is trapped in a cruel dilemma: if he remains true to the impulses of his art, however dark these may be, he faces what he calls the agony of “eternal separation from his wife and children”. But if he succumbs to authoritarianism and self-censorship he knows he will be miserable. “I feel good about my art,” he says. “I feel like it is part of my identity. I don’t want to have to make a choice between the Mormon Church and my work, but if I do I will be on the side of art, even though I still have my faith.”

This is painful, too painful: already cracks are appearing in the once smooth surface of his family life. His wife, Connie, comes from a doctrinally more austere Mormon family than Evenson’s, whose parents were the only Democrats in his neighbourhood while he was growing up in Provo, Utah. He and Connie married “when we were in our early twenties because we were brought up thinking that is what you did”. His eldest daughter Valerie is six, and his youngest, Sarah, is four.

In common with all Mormons, Connie believes that a “man’s heart is revealed in his art”. Evenson says: “She can’t understand why I write as I do. Though she has a French degree, she does not have the same kind of literary background as me. We are committed to each other, but what I am doing is causing her a lot of pain. We don’t argue, but we talk about it, we debate about what this means to us as Mormons. But she feels that if I continue doing a certain kind of art then, in essence, I am betraying her.”

Does he believe that? “I kind of do and I don’t,” he says, lowering his head. He is a big man, with huge hands and thick red hair worn in a ponytail. With his distressed jeans and wispy goatee beard he looks more like a farm labourer - or perhaps a roadie for a rock band - than the sophisticated literary intellectual that he is. At times, his voice scarcely rises above a whisper. It is hard to believe he is the author of work of such terrifying nihilism - work described as “morally absent”. But, of course, there is no such thing as moral absence: even amorality is a cannily ethical position.

Certainly that was the feeling among the hierarchy at Brigham Young, the Mormon university in Provo where Evenson taught literature and creative writing but from where he says he was “forced to leave” after a female student wrote an anonymous letter alerting the authorities to the extreme material in Altmann’s Tongue .

“This man has an obsession with murder,” she wrote. “There are descriptions of can nibalism, incest and serial murder…(reading the book) I feel like someone who has eaten something poisononus and is desperate to get rid of it. As Latter-Day Saints and disciples of Jesus Christ I believe we have a responsibility to use our gifts to bless the world with truth and hope - not to revel in darkness and degredation.”

In his defence, Evenson says he wishes not to glamorise, but to confront, violence. “When I was a boy growing up in Utah, I was disturbed that most of my peers felt that they could justify seeing an adult movie as long as it was ‘only violent’ rather than depicting sex. Violence, they thought, was somehow acceptable and entertaining but they had a real problem with sex. In Mormonism there is an emphasis on talking only about what is good in life. So you end up making a space where evil can occur unimpeded. I want to expose people to the darker side of life, to challenge them, to show that evil is part of this world.”

After much anguish and vilification, Evenson took a job last year at Oklahoma State University - because he felt “there was no place for me at Brigham Young; they wouldn’t support me in my work”. Appalled that fellow Mormons found his fiction unconscionable, he felt trapped and harassed in Provo. “I felt like an outcast in my own town. I would go into restaurants and people would look at me as if I was dangerous. It kind of got to me.”

The clash between Evenson’s literary sophistication and the uncompromising literalism of many Mormons has a compelling modernity. For Mormonism is one of the fastest growing religions in the world. There are almost ten million worldwide, half of whom are in the United States, clustering in Salt Lake City, Utah, where the Church has its headquarters.

The sect was founded, in 1830, by Joseph Smith as the Church of Jesus Christ of Latter-Day Saints in Fayette, New York. Part of its appeal is its intense exoticism: Smith famously claimed that Moroni, an ancient American prophet, appeared to him revealing the existence of a hidden gospel engraved on golden plates and buried 1,000 years earlier on a hill near Palmyra. These were transcribed as the Book of Mormon, and together with the Christian Scriptures form the basis of the faith.

When Evenson was 19 he spent two years in France, Switzerland and Mexico doing the missionary work required of every young Mormon. “I remember knocking on doors wearing these dark suits. It made the religon seem terribly corporate. The thing about Mormonism is that the conversion process goes on even for the dead. It is very inclusive.”

Evenson is working out a complex literary destiny in the desert landscape of Utah. Tied through a quirk of birth to a religious community that grows ever more trenchantly confident with each new convert, he feels “lost and confused”. His next book, Father of Lies, explores another Mormon taboo: child abuse. Structured as a pyschoanalytic case study, it draws on actual, previously repressed cases of the abuse of young boys by Mormon lay clergy.

“Sometimes I wake up after a nightmare thinking I must be crazy to publish this book, because I know they will excommunicate me for doing so,” he says.

He approaches this prospect with lucidity and gloom. “In my more rational moments I’m not sure the Mormon authorities can dictate what happens to me after my death. The Church is at a point where it can become even more repressive, or embrace a new openness. I’ve thought about what I’m doing, I’ve prayed for guidance. If I get excommunicated, my hope is that they might take me back in at a later date.”

You know that he knows that this may be a forlorn hope indeed.