ZONE OF FIRE by Conrad Detrez (Harcourt Brace Jovanovich: $17.95; 266 pp.)

A FRENCH SCIENTIST ARRIVES in Managua in 1979 to study his specialty--volcanoes--of which there are 33 in Nicaragua, a dozen of them active. “I worship stones,” he confesses, and devotes pages to the bizarre configurations of Nicaragua’s quake-wracked capital. In the first third of his novel “Zone of Fire,” Conrad Detrez uses the second person (“Clearly, you think, nothing is so wonderful as stone”) to identify his narrator as a dispassionate observer of the Sandinista revolution. Through this awkward device, we learn that the volcanologist is an unhappily married intellectual who suffers from the Old World disease of ironic detachment from human affairs. “They’re extinct . . . sir,” he protests to a policeman who advises him to go study his own country’s volcanoes. To which Somoza’s minion rightly replies, “If everything is going extinct there, too bad for you--it is not our fault.”

But the fire zone’s revolutionary ferment proves to be as compelling as its geological fireworks, and the introverted volcanologist becomes enmeshed in the lives of half a dozen characters he meets in his pension. In the second third of the book, told in the omniscient third person, we follow the fates of these characters as they are drawn into La Revolucion.

There is Ignacio, the Guatemalan militant priest, who seeks redemption by quoting obscure Mayan texts and hankering after mestiza whores. Ignacio dies, shot through the eye, in an armed clash with the National Guard. His colleague, Comrade Superior, a liberation theologian and a dead ringer for Nicaragua’s foreign minister Father Miguel D’Escoto, is among the few revolutionaries who holds on to his skin and his sanity and becomes a powerful minister after the victory. Leonor, a feminist and former journalist, becomes editor of the Sandinista Front’s official newspaper. In a key discussion with Comrade Superior after the Sandinistas have taken power, she tells the narrator, “The Revolution is no longer a matter of the heart. The heart mattered before we took power.” To which Comrade Superior adds ominously, “Today, the heart is the enemy.”

The narrator’s own ambivalent attitudes are dramatized in the lives of the two central characters, the brothers Alvaro and Abel. Abel, who inevitably evokes his biblical counterpart, falls in love with a young man nicknamed Chino, who enlists in the National Guard in order to support his ailing mother. Poverty is the common denominator here, and it fuels uncommon expectations. Alvaro’s three fighting cocks are reflections not only of his macho code and lust for conquest; they support the respectable fiction of his engagement to a middle-class girl, Gladys, whom Alvaro sodomizes and then abandons. After he joins the Front, Alvaro spends most of his money on whores, whose brothels become the nurseries of the revolution (and later on, of the counterrevolution).

After his violent death, Abel becomes a Sandinista martyr. And he does seem almost saintly compared to the driven, unscrupulous Alvaro, who is “made for terrorism.” Abel is drawn to socialism because it is “an equitable pigsty” that can accommodate his sexual deviance so long as his revolutionary actions are “correct.” But Alvaro sees Abel’s homosexuality as a stain on the family honor. When he catches him making passionate love with Chino, he whips out his pistol and shoots him. Later, he brazenly denounces his brother as a “blot on the Revolution;” but the members vote to expel Alvaro from the Front, and he blows himself up in a kamikaze attack on a high-ranking National Guardsman.

In an Epilogue to “Zone of Fire,” the volcanologist returns to Managua after the Sandinista triumph to track down his surviving friends. His very French skepticism is in part reinforced as he dissects the “Sandinizing” process that threatens to turn the blood and sacrifice of his friends, and of the 50,000 other casualties, into a cruel parody of revolution. But in the end, the volcanologist, an heir of Robespierre, suffers his own baptism by fire through his awakened compassion and experiences a moral rebirth.

The central story of “Zone of Fire” is compelling, but the outsider’s perspective never penetrates the skin of the two brothers, or of the other key personages. (The repressive Somoza dynasty, which dominated Nicaragua for two generations, is represented by a mounted bronze statue.) The book lacks the intensely lived quality of, for instance, Omar Cabezas’ “Fire From the Mountain,” a first-person testimony by a revolutionary who is a minister in the Sandinista government.

The larger theme of “Zone of Fire” is the dialectic between the romantic ideals and passions released by the revolution, against its tendency to abstract itself into a heartless ideology that ultimately cannibalizes all but its most disciplined or ruthless participants. But the dialectic is not carried through to any conclusion.

The truth of Nicaragua is that the Revolution is larger than any of its component parts, of which the Sandinista Front was only the largest and best organized. “Zone of Fire” makes no mention of the assassination of publisher Pedro Joaquin Chamorro, an opponent of Somoza’s who galvanized resistance in the middle class. It does not mention spontaneous uprisings like the ones in Masaya and Monimbo, where youths flung themselves bare-fisted on the National Guard’s tanks in 1978, and sparked a popular revulsion against Somoza. “We made the Revolution,” a youth of Monimbo said in 1983, on the occasion of the Pope’s visit to Nicaragua, “and if the Sandinistas fail us, we will make it again.” In a sense, President Reagan is right when he says that the Sandinistas represent a fraction of Nicaraguans. But after the terrible price the Nicaraguan people paid to overthrow Somoza and his National Guard--bequeathed to them by the U.S. Marines--who but the most cynical or misguided observer would suppose they would welcome back their former oppressors, in their shabbily transparent “Contra” disguises?

Detrez may argue that these issues fall outside the scope of “Zone of Fire,” but without addressing them, this novel remains an absorbing but truncated portrayal of one of the seminal events of our time.