The South Bronx was imprinted on national consciousness when President Jimmy Carter, after surveying through the unbelieving eyes of Plains, Ga., declared to an assemblage of television cameras that he intended to do something about it. It was the polite thing to say -- Mr. Carter may well be the most polite president ever elected -- but while we wait for the miracle to be wrought, a growing host of native New Yorkers like myself suspect that the most sensible thing to do is simply plant a large bronze plaque in the area. Such a tablet would explain to visiting archeologists that they are here viewing what can become of a thriving urban neighborhood when rapacious landlords, a high-spirited lumpenproletariat and a series of fuzzy-minded city administrations are given their way with it.

The South Bronx, literally a burntout case, is a sort of paradise for arsonists of both the professional and amateur persuasions, and it is a case of arson that triggers the action in "Summer Fires," an unusual and sometimes powerfully effective novel by Bob Reiss. The book goes well beyond offering the standard tale of suspense; it is provided an extra dimension by the author's evident depth of feeling for his subject. This is his first novel, but already he is wise enough to eschew sermonizing on the causes of a condition in favor of a graphic picture of the condition itself.

Miles Bradshaw, his protagonist, is, in the Graham Greene sense, a burntout case himself. A once-successfl Park Avenue lawyer, he unwittingly caused the deaths of his wife and child in a fire, and now, traumatized by the disaster, he leads a solitary guilt-ridden life in the South Bronx, occupying a room and working for one of those pathetic, underfunded tenant's-aid agencies established more to make a presence in the neighborhood than to lend succor to its beleaguered tenancy.

Bradshaw sees from his room a building fire, apparently involving the murder of a child, and is driven to investigate it. Herein lies the tale, because that particular fire has international ramification, and Bradshaw soon finds himself up to the Adam's apple in a private war against a glittering champagne-and-caviar crew of desperadoes ruled, as we quickly learn, by a Korean magnate named Wot Chow Trench who, despite our temptation to think otherwise, has no pretensions to being the second coming but does yearn for a certain piece of imflammable South Bronx territory.

Bradshaw, emotionally sustained by the beauitful woman next door, Elena Moreno, and alternately supported and harased by a South Bronx youth gang and a fire marshall named Goldstein (a superbly drawn character who knows and distrusts Bradshaw after having investigated the deaths of his wife and child), moves along a dangerous course to the exposure of Trench and company, and their destruction. The rules of the game forbid my revealing what Trench wanted of the South Bronx. Suffice in to say that his plan, if put to work by respectable, well-intentioned people like you and me, would assure not only instant salvation for the South Bronx but for the entire economic structure of the United States.

In a way, Reiss seems to have been betrayed by his capacity to write so well in two entirely different modes. Thus he portrays the South Bronx with bitter conviction and presents his international villains with easy expertise, but in one mode he is dealing with an agonizingly real world and in the other an entertainingly make-believe one, and these twain can never truly meet.

Yet, talent will out, and Reiss, evidently a born storyteller, invests "Summer Fires" with a jet-propelled momentum that never flags. No matter how much I balked at various gaudy implausibilities of the narrative, I found myself reading it at a great clip with a keen, if sometimes wary, interest in what was going to happen next, and I suspect that the largest part of the book's audience will share precisely that experience.

I hope Mayor Edward Koch, incumbent guiding genius of New York City, will be one of that audience. The book's ultimate revelation may not offer him a workable solution to the city's problems, but -- the quintessential wish-fulfillment -- it should certainly brighten his otherwise troubled dreams for a long time to come.