Sympathy, or at least empathy, for the Devil seldom fails as a novelistic formula. Virtue may inspire, but evil fascinates. Most fascinating of all, perhaps, is political evil -- the sort of programmatic perfidy that doesn't just harm individuals but roils the flow of history itself. For all its richness as a subject, such large-scale wrongdoing rarely gets much play in the work of North American writers, who tend to favor stories of private crime over tales of public villainy. Recent events may change this cultural emphasis, but for now one has to look abroad, to talents such as Mario Vargas Llosa, the prolific Peruvian essayist and novelist, for the lowdown on organized evil in high places.

''The Feast of the Goat'' takes its title from the nickname for Gen. Rafael Trujillo, the dictator whose 30-year reign of terror in the Dominican Republic ended with his assassination in 1961. Trained by the Marines, and long an anti-Communist client of the American government, Trujillo became, in the last years of his life, an isolated pariah beneath the palms, harassed by bad press and economic sanctions. Like the younger Castro, whom the clean-cut, right-wing general despised, Trujillo encouraged a cult of personality that made him more than a simple head of state. The state was his body. Its limbs sprang from his trunk.

And from his groin, if Vargas Llosa has it right. Though we meet him in the last hours of his life, old, embittered, ailing and besieged, Trujillo still fancies himself a sexual superman -- a Valentino with epaulettes and sidearms. In a country of legendary playboys like the inhumanly well-endowed Porfirio Rubirosa, Trujillo understands that power flows not from the point of a gun alone but from the tip of a phallus. He holds his subjects in an erotic spell. The women he beds -- mistresses, underlings' wives and random party girls procured for him by a former male model who also advises him on grooming and wardrobe -- are magical surrogates for the body politic. Therein lies the irony of his authority. Though he see himself as a soldier and a rationalist and regards the Haitians across the border as heathens to be purged and murdered, Trujillo is, at heart, a voodoo priest. The ritual penetration of female flesh is the mystical basis of his rule.

Assisting Trujillo is a cast of zombies that the author must have given himself nightmares raising from the crypt. By alternating fatherly affection with calculated silences, the dictator fosters a chronic, low-level panic among his spiritually gelded lackeys. The scariest is Col. Johnny Abbes Garcia, the Goat's intelligence chief, who dabbles in Rosicrucian hocus-pocus and claims to be able to read his victims' auras even as he burns them with lighted cigarettes and jolts them with voltage from an electric chair. Abbes Garcia is an archdemon of great refinement, a connoisseur of terror who prides himself on killing within a budget and on schedule. His henchmen scoot about the capital city in identical black Volkswagen Beetles -- a touch of macabre, comic genius. For Vargas Llosa, Abbes Garcia is the dictator's perfect psychic instrument, an externalized id. The pair's sinister duets, shot through with the uneasy familiarity of shrunken host and swollen parasite, are some of the book's most vivid, troubling scenes.

The novel promises fireworks from the outset as the dictator's enemies load and point their guns, but the author is in no hurry to pull the trigger. He fills the pregnant pause with protocol -- the phone calls, meetings, meals and little ceremonies that, taken together, give power its shape and form. Trujillo is a creature of routine, maniacally fussy about his dress and hygiene. His government and his country may be a mess, simmering with intrigue and frustration, but, by buttoning his shirt just so, he's convinced that the chaos can be contained. Unfortunately for Trujillo, he's slipping physically: he can't control his bladder, and he's horrified. As one who identifies his personal regimens with the larger condition of his regime, he senses that disaster will come soon. When he wets himself during a formal luncheon, it's as though rebel commandos have stormed the palace.

Vargas Llosa fills in Trujillo's daily calendar with copious notes on modern Dominican history. The transitions from present to past are sometimes awkward. To provide an excuse for expository digressions, characters ask questions of one another that they already know the answers to. Dialogue segues into reminiscence, not always naturally. The most distracting of these excursions involves the present-day homecoming of one Urania Cabral, the daughter of a former Dominican senator who gave his all to Trujillo but then lost favor. Urania, who is now a lawyer in New York, left the country as a schoolgirl and has returned to visit her father's sickbed and get something big and mysterious off her chest. Her major revelation, when it comes, is a typical melodramatic shock having to do with sexual abuse, but it pales somewhat next to the novel's grisly scenes of dungeon interrogations and torture sessions. Talky, introverted and atmospheric, with lots of mediation and self-analysis, the Urania sections seem to be on loan from another sort of book.

But a story in motion tends to stay in motion, and the fundamental momentum of the tale instantly recovers from the small trip-ups. In this crackling translation by Edith Grossman, Vargas Llosa's Trujillo is a riveting creation -- a corked volcano of vulgar, self-pitying rage who demeans his aids with mocking nicknames (he calls the cerebral Cabral ''Egghead'' and refers to his alcoholic legal adviser as ''the Constitutional Sot''). The foundation of his position, for Vargas Llosa, isn't simple ruthlessness, but his talent for provoking self-doubt in others. Trujillo is a Nietzschean vampire, sucking up others' wills into his own. Oppression is a transfusion; it takes two. Oddly, Vargas Llosa's Trujillo sees himself as having gotten the short end of the bargain. He whipped his pathetic homeland into shape, modernized its attitudes and highways and in return he got -- old. It's quite an insight. The tyrant must rationalize his rule with fantasies of self-sacrifice and victimhood.

The general's bloody end is never in doubt. The suspense comes from wondering who will fill his boots. When Trujillo falls, the novel revs up, burning supporting characters as fuel. The nation's designated liberator is Gen. Jose Rene Roman, whom the plotters are counting on to seize the reins but who, in a puzzling collapse of nerve, slips into a paralyzed passivity at the fateful moment. Roman's befuddlement is a masterstroke -- the nation's destiny is within his grasp, but his arms remain at his sides. They've atrophied, unaccustomed to acting on their own. Vargas Llosa shows that freedom begins in the soul; it can't be won with bullets. In another disaster, a hospitalized co-conspirator finds himself dreamily giving up comrades' names to a mesmerizing Abbes Garcia. Trujillo is dead, but his legacy lives on in his enemies' numb, evacuated spirits.

An unlikely savior emerges from the sidelines. Joaquin Balaguer, Trujillo's puppet president, is the consummate faceless functionary -- a mild-mannered poet who's lurked about the story without ever making much of an impression. He goes from cipher to leader in a few pages -- a transformation of dazzling subtlety that has to be read twice to be appreciated. In a dictatorship, Vargas Llosa suggests, remaining self-possessed is the great challenge. While the fiery partisans combust around him, the calm Balaguer reassembles the republic. As a figure of the ideal politician, he's a curious case -- he lacks any discernible social vision and tolerates the crimes of right-wing goon squads rather than jeopardize his own position -- but it's clear that we're meant to admire him, in context. Balaguer is a room-temperature man, an antidote to the volatile Trujillo. In a country and a story swarming with villains, where even the antagonists have antagonists, pragmatism is akin to heroism.