The door swings open on the conscience of a nation.

Brace: One expects no less than a roar of thunderous rectitude and the fearsome mien of an Andean Ezekiel. This is, after all, Mario Vargas Llosa, outspoken abominator of political violence, scourge of dogmas left or right, sought-after journalist/commentator, heartsick patriot ("Peru is for me a kind of incurable disease") and globally acclaimed author -- most recently of "The War of the End of the World."

But the small, trim man standing in this sun-splashed hotel suite has the face of a nightclub rumba king, a cheery tenor voice, delicate manner, pale green slacks. And a sense of humor that can shift abruptly from the profound to the gruesomely cavalier:

"If you're a writer in a country like Peru or Mexico, you're a privileged person because you know how to read and write, you have an audience, you are respected -- even by people who repress you and sometimes put you in prison or even kill you. In fact, if you are killed because you are a writer, that's the maximum expression of respect, you know."

And he laughs! Two loud staccato yaps sharp as the crack of a gavel, subsiding in a fast tumble of chuckles. As if mirth, like other inflammatory passions, were a thing to be indulged only with caution.

It's certainly rare in the new novel, which The Washington Post says makes most American fiction look "very small, very private, very gray and very timid," which The New York Times calls "powerful and haunting," which James Wolcott in Vanity Fair deems "one of the bloodiest, cruelest books I've ever read, and one of the most enthralling."

Its 568 gore-sodden pages depict in epic breadth the civil war that convulsed Brazil at the end of the last century. The date is 1897, the nation has only lately acquired republican government, and a fanatic millenarian preacher, known as the Counselor, is recruiting followers to his gospel: ascetic worship, communal property, Christian hegemony over the "Antichrist" of the secular state, and the imminent end of the world. Government leaders, needing an excuse to affirm the power of their fledgling regime and projecting their own fears onto the situation, delude themselves into believing that the Counselor's burgeoning band of credulous peasants, deformed outcasts and criminals must conceal a British-funded monarchist plot. At first, 100 soldiers are sent to destroy the "rebel" camps in the desert escarpments of rural Canudos. Then 500. Then 1,200. Each foray is humiliatingly crushed by the Counselor's ragtag forces. Finally 4,000 troopers with heavy artillery arrive and obliterate the cult, leaving nearly 40,000 dead.

Violent subplots burrow through the flashback narrative: A country woman is raped by a British anarchist and her husband spends all he has -- his life included -- to avenge his honor; an itinerant anarchist-phrenologist who has indentured his life to scientific rationalism confronts the heart of unreason; a journalist must pass through horror to find the meaning of the war; a grandee's ruin drives him to explode in long-repressed passions.

The slaughter might seem a mere lurid anomaly -- one still-exploitable vein of melodrama in the brutal topography of Latin American culture. But no:

"I decided to write this novel," Vargas Llosa says, voice shifting to a professorial timbre, "because in the history of the Canudos war you could really see something that has been happening in Latin American history over the 19th and 20th centuries -- the total lack of communication between two sections of a society which kill each other fighting ghosts, no? Fighting fictional enemies who are invented out of fanaticism, out of religious or political or economic blindness! This kind of reciprocal incapacity of understanding what you have opposing you is probably the main problem we have to overcome in Latin America if we want to civilize our countries."

(This is no paraphrase: Vargas Llosa's command of English vocabulary is astonishing; and if momentarily stuck for a word, he will elevate his gaze as if to some celestial word-hoard, unfocus his eyes and return promptly with an elegant $10 Latinism. Thus, apparently searching for "cohere," he comes back with "agglutinate," each foray ending in a triumphant little "No?")

Such pronouncements have made Vargas Llosa -- winner of numerous literary awards and oft-rumored candidate for the Nobel Prize -- renowned as a spokesman for Latin American affairs. Though best known here for his previous novel, the quasi-autobiographical "Aunt Julia and the Scriptwriter," at home in Lima he is a virtual media conglomerate: President of PEN (the international writers' and editors' organization) from 1976 to 1979, he has also found time to host a weekly TV culture-talk show called "The Tower of Babel," write a hit stage play and see "Aunt Julia" transformed into a popular TV series.

Even "War" got its start in the movies. Ten years ago, a Brazilian filmmaker asked Vargas Llosa to write a script on the subject. He read an account by Euclides da Cunha, a historian who had traveled to Canudos with one of the military expeditions. De Cunha arrived freighted with the official preconceptions. "But he had an incredible aptitude, very infrequent in Latin American intellectuals: After the massacre he was embarrassed and confused and he started to think it over again. And he decided he had been wrong, that many people had been wrong," and wrote a history of the war as "a kind of examination of conscience." The film project died, but the story stuck. Vargas Llosa wrote a draft of the novel, then went to Canudos and to the 25 villages where the Counselor is said to have preached. "Everybody has a great uncle who was there, a relative who died there," and "the Counselor is still a living presence, people talk about him."

"I have never been so fascinated with a story," he says. "You can't imagine how anguished I was at any given moment. I felt totally lost. So many episodes, so many characters, but I couldn't find a center." It took four years, the last of which he spent in Washington as a fellow at the Woodrow Wilson Center. At first, he was apprehensive: "I had been told it was the most dull city in the States. But I think it's a calumny -- it's very alive. I was envious because I would like a Latin American capital to be a place where so many Latin Americans from as many perspectives and positions come to discuss their affairs." Moreover, in researching the book, he had ransacked Brazil for copies of an outspoken local paper of the period and had found only one copy. But at the Library of Congress, "there was the whole collection!"

The book was published in Spanish in 1981. There was no English version until this year "because the translation took a lot of time." No wonder: His present translator, an American woman named Helen R. Lane, lives in a tiny French hamlet and "I have never seen her. We communicate only by letter," shuttling lists of words and phrases back and forth. "I think she's never been in Latin America -- but her command of the Spanish is extraordinary."

The novel will further his reputation as a humanist who reviles with equal vigor tyrannies of the right or left (is there really a difference, he asks, between "good tortures and bad tortures"?) as well as the ritualized violence he limned so powerfully in his first story collection, "The Leaders" (1959). The redemption of "honor" by blood, he says, "is not an anachronism, you know." After a lecture recently, he took questions from the audience. "And a day later, a gentlemen who was one of the questioners sent me un testillo for a duel because he felt that I had offended him with my answer. Now I am very cautious. I sent him a book with a funny and friendly sentence written in it, and his honor was restored, you know." Again, the barking laughs.

Indeed, his life seems one long rejection of successive ideologies and authorities. His father and mother had divorced before he was born in 1936, and he was raised in Bolivia by relatives, returning to Peru in 1945 after his parents were reconciled. His father was living in Lima, and young Mario found himself "submitting to the discipline of a very severe man who was a stranger to me."

He found solace in books. "I started to read novels when I was very, very young, and I was disappointed when they were finished. So the first things I wrote were continuations of books that I had liked -- 'The Three Musketeers,' even 'Moby Dick!' " Again the sharp barks of laughter. To this day, "I have always liked long novels," and he greatly admires the 19th-century masters. "I think the novel has a natural disposition to proliferate. Unlike poetry, in the novel quality and quantity are related. It's time flowing and that means quantity," the space "to develop a whole world."

His father found out that he was interested in writing, and fearing for the boy's financial future (and his manhood: "the belief that poets are homosexual is still very widespread"), he enrolled his son in a strict military boarding school. The boy found it a "microcosm of Peruvian society," replete with rigid hierarchies and physical cruelties. He thought it hellish, but "it helped me very much -- I discovered what a totalitarian structure means for an individual. I think I developed a great taste for freedom." (The 1963 novel he derived from the experience, "The Time of the Hero," would bring him his first fame. And his first reprisal: When it appeared in Peru, 1,000 copies were burned in public by military officials.) Meanwhile he was fueling his own apostasy with books, which became "an escape," a way of "compensating for everything that saddened and disgusted me." (Not surprisingly, he now speaks of the novel genre as "a kind of god-killing," constituting "a rectification of the real reality, an act of rebellion against the Creation" by the posing of a counter-cosmos.)

At the same time, he was learning other forms of subjugation. "We had a real dictatorship in Peru then" -- under Gen. Manuel Odria, who in 1948 overthrew Jose Luis Bustamante y Rivera, a cousin of Vargas Llosa's grandfather -- and "my family had been brutally persecuted. So I became sensible to political problems." And by 1952 he was working part time for a newspaper, suddenly "in touch with people and problems that were so different. If you were a middle-class boy, you were so alienated from the life of an Indian, say, or a worker. That was a great help when I started to write, because it gave me a vision of my country much more diverse and complete than if I had remained secluded in my minimal world.

"My family had been very prosperous before I was born. But they went bankrupt with the famous crash of '29. Since then we had been living as a middle-class family with many economic problems, but with great dreams of this splendorous past. I became a rebel very early. I became very critical of the bourgeoisie, of the terrible social inequality, the racial prejudice." Whereas "all the middle-class boys went to the Catholic university or a private school," he chose San Marcos, the public university, "because the low-bred people were there, and it was very rebel, very left-wing." As a student he worked for newspapers and Radio Panamericana (the basis for "Aunt Julia"), and even joined a proto-communist group.

"Yes, I was a militant for one year," but "I was saved by socialist realism -- the esthetic theory of the Communist Party during the '50s. I was so critical of that kind of literature that I became a dissident and broke with the group. Afterwards I became more intellectually separated. But at that time it was literary, esthetic. I couldn't accept that Andre' Gide, whom I admired, or Camus or Kafka were just propagandists of imperialism. I remember a discussion in my cell about literature. I defended Gide and one of my comrades said, 'You are subhuman -- a decadent pervert!' " But by then he was deeply interested in literature, especially Joyce, Malraux, Proust, Hemingway and, of course, Faulkner, in whose eccentric, caste-ridden, myth-haunted Yoknapatawpha County Vargas Llosa found an apt counterpart to his own land. Beyond those, "I am not so familiar with Americans," though he admires Carson McCullers' work, Truman Capote's "Other Voices, Other Rooms" (but "not what he wrote after") and Norman Mailer's "The Deer Park."

He took a scholarship to the University of Madrid in 1958, began working on a PhD, then moved to France and England -- returning to Peru only after constitutional government was restored in the 1980 elections. Without the years abroad, "I would have been a completely different writer," never learning the "monotonous discipline" of the craft. "Had I stayed in Peru, I would have been what I was before I went to Europe -- a writer of weekends and holidays. Probably much of my time would have been devoured by other activities. But in Europe I realized that I must organize all my life around this project, subordinate everything to this" and forsake the expectations of his family and class. "It was unthinkable at that time to consider literature as my occupation."

He believes that "I have lived far enough away from my country to not be limited by a parochial vision of Peruvian problems." Yet "it is impossible for me to become an exile. I am marked by my country, my language, my society. I am an outsider -- in two worlds simultaneously -- and this is good for literature, no? It gives you perspective, but it also gives you roots."

A happy combination in Latin America, where, he says, writers are obliged to serve as a "social conscience, are still considered people who can make a contribution to the solution of social and political problems. Maybe it's naive, but it's true." Thus "it is a moral obligation of a writer in Latin America to be involved in civic activities" -- often at tremendous cost to writing time, which is why he spends some private weeks in Europe every year.

Though he concedes that encumbering an author with such grandiose responsibility is a "romantic" notion, he is nonetheless contemptuous of those he feels fall short. He will not tolerate foreign writers -- often driven by "an unconscious prejudice, an inchoate sentiment, a sort of visceral racism" -- who propose solutions for his region that they would not accept in their own. Hence he castigated Gu nter Grass in The Atlantic for arguing that Latin American countries could solve their problems only by following "the Cuban example," and further ridiculed the notion in "War" through the character of Galileo Gall, the English anarchist/phrenologist who projects on Brazil "everything that is not possible in his own country, an ideal of society and revolution which had been totally defeated by reality."

He is even harder on Latin writers. Among them: Nobel laureate Gabriel Garcia Marquez, once Vargas Llosa's close friend and the subject of his doctoral dissertation. But they split over the Colombian's support for Cuba. Vargas Llosa also had been a partisan until he attacked Castro in 1971 for jailing the poet Heberto Padilla.

Many Latin American authors, he says, have used their influence "not to fight against fanaticism, but to give respectability to fanatic positions and ideas. Propagating, for instance, the idea that the only way to fight the structural inequity is through violent solutions -- which has added so much to the daily massacres. Many, many writers have avoided the reformist i.e., moderate way as something despicable -- a fake solution."

Just as the Counselor's diverse and motley throng was exploited and mislabeled by self-serving forces, Vargas Llosa believes that the sporadic guerrilla attacks now plaguing the Peruvian Andes "are not 'peasant movements.' They are born in the cities, among intellectuals and middle-class militants." And the peasants are merely "coerced by those who think they are the masters of history and absolute truth."

Witness the recent incident in which the grisly paradigm of Canudos was reenacted again. Early last year, Indian peasants in the remote Andes killed seven members of the Sendero Luminoso ("Shining Path"), a Marxist guerrilla group trying by terrorism to impose "revolutionary" practices on mountain villagers. The Peruvian military touted the event as "good news," proof that peasants were resisting "subversive criminals." But when a group of eight journalists arrived to probe the incident, they too were massacred. Vargas Llosa was named to a commission sent to investigate the second slaughter, and found it an enigma: Conducted with "magical and religious overtones" by people ignorant of or indifferent to laws of the state, and by no means evidence of a "peasant movement" for or against the guerrillas.

Instead, as he wrote in The New York Times Magazine, it was "an encounter with another time, a gap of centuries mere language could not bridge" -- including the same miscomprehension of motive, the same retrofitting of fact to preconceptions that had characterized the Canudos war. "The fact is that the struggle between the guerrillas and the armed forces is really a settling of accounts between privileged sectors of society, and the peasant masses are used cynically and brutally by those who say they want to 'liberate' them."

In "The War of the End of the World," the nearsighted journalist-narrator (who ironically has the clearest vision of the madness), says of those involved in the Canudos war: "They could see and yet they didn't see. All they saw was what they'd come to see. Even if there was no such thing there . . . How to explain that?"

"People's credulity," replies the Baron de Canabrava, a genteel conservative ruined by the rebels, "their hunger for fantasy, for illusion."

The theme continues into "A History of Mayta," the book he is finishing now, though it will be "a very different kind of novel, shorter, concentrated in one character. But it is about an attempted rebellion by a group of young people and a young officer in the '50s. I'm trying to find the roots of the present political violence. But it's also about the interrelation of fiction and politics. It is wonderful to invent utopias in fiction. But in politics it can be very damaging."

And for a moment the handsome face rumples, pulled at once between a grin and a frown. "In Latin America, we have this drive to use too much fiction in our politics -- and too much politics in our fiction!"