WHEN PAUL STEWARD, former Peace Corps volunteer and current CIA operative, is transferred from his backwater posting in Honduras to Chile in 1973, it almost immediately becomes obvious that someone in Langley has made a mistake. For Steward is the prototype of the disillusionist idealist, the liberal manque, who has developed a loathing for his fellow agents as well as for himself.

Nevertheless, in this rather bitter novel about the CIA's involvement in the overthrow of Salvadore Allende's government, Steward goes methodically about his job, which largely consists of fingering those leftist Chileans who are to be clapped in jail once Allende is toppled by the military.

Steward despises his CIA colleagues, his undercover role, and the cynical right-wing Chileans with whom he is forced to deal in his cover job as correspondent for an almost mythical Los Angeles-based newspaper syndicate, which is actually a CIA front.

The one bright spot in Steward's otherwise dismal existence is his reunion with Marisa Caseauz, the young Chilean woman who taught him Spanish in New Mexico when he was training for the Peace Corps nearly a decade before, and with whom he once had a brief but steamy affair. The romance flourishes again, only to die quickly killed by Steward's unwitting betrayal of Marisa.

Interventions is Patrick Breslin's first novel and, perhaps wisely, he does not take us into the higher reaches of the Allende government or its military opponents. Instead, we are given a well-drawn portrayal of some of the ordinary Chileans who were near the top of the hit list that had been computerized by the CIA for the convenience of the military.

In two or three almost searing scenes, Breslin describes the suffering of those who were unlucky enough to be confined in the infamous National Stadium in Santiago after Allende is killed. Among those imprisoned is Marisa. What happens to her is not pretty.

Near the end of the novel Steward, now shattered, reviews his years with the CIA. They had slipped, he thinks, like "tramp steamers in the fog, while he tried to force some meaning into what he did, some way to convince himself that lies and bribes, corruption and betrayals were building the foundations for democracy and development. And what had it all led to, his soldiering in the shadows. Nothing beyond what embassy cables called a good climate for investment."

Author Breslin apparently knows Chile well and seems to be extremely fond of both the land and its people. His eye for detail is excellent; his descriptive powers interesting; his dialogue serviceable. His sympathies for Chile's poor and oppressed are unabashed.

And once again, the CIA serves as one of fiction's most useful and durable villains. Its operatives as drawn by Breslin are an insensitive lot, manipulative, ambitious, cruel, and even a bit dim. They are also strangely subhuman.

This is not the story of the grand design that emerged at the Senate hearings on the CIA's involvement in Allende's downfall. Instead, this is a nuts-and-bolts approach -- what the CIA did to whom, and how it affected the lives of those Chileans and Americans alike who were unlucky enough to brush against it.

It's a cautionary tale, well written, and curiously sad. The young woman, Marisa, emerges as an admirable heroine, Steward as something of a wimp, far from tragic, but too confused to be truly despicable.

As for Chile, well, Chile is the novel's true victim. It's a country that deserves far better than it has had, or apparently, can expect.