I DOUBT whether Faulkner understood his Yoknapatawpha County any better than John D. MacDonald has the measure of the "Redneck Riviera," the stretch along the Gulf of Mexico from the Florida panhandle to the Texas border. People who haven't read MacDonald -- and ought to -- may think of it as Body Heat territory, but he invented it as a subject for art. Indeed, the popular film was pure MacDonald -- without the credits.

What goes on along this sultry several hundred motel- and condo-lined miles is guys "doin' bidness" with each other. "Bidness" is principally real estate development; land deals; despoliation in the name of commercial progress. This is the stuff to which MacDonald returns in Barrier Island, and returns -- I am happy to report from this armchair -- in fighting trim.

In this instance, the profitable prize which the bad guys are after is incarnated by kidney-shaped Bernard Island, a sliver about ten miles out in the Gulf, in the storm belt, which developer Tucker Loomis sees as the catalyst to gull Uncle Sam -- through the National Park Service -- out of around ten million dollars in condemnation money. It's a clever scam, lucidly set up and explained by MacDonald; Loomis is a power in the mainland town of West Bay, one of those polities -- one-third trailer park, one-third industrial park, one-third luxury "estates" development -- in which the big boys, the bankers, lawyers, construction heavies, get together on Saturday nights and cut up the common weal over table-stakes poker.

It gives MacDonald a chance to delve into the pathology of opportunism, and that he does, adroitly and insightfully. It's woven into a story that moves right along, with a variety of nicely individuated, well-sketched characters intertwining effectively. MacDonald wants us to know who and what his characters are, and how they got that way. In a book that's making the point I think this one is, that's essential. It's not the sex or the violence, then, or the mechanics of the scam, or the technology of putting the fix in, that provides the focus for the reader. All those aspects are here, to be sure, and in good supply; after all, MacDonald established his royal warrant in these areas a long time ago, maybe even as far back as 1953, when I recall plucking the first book of his I ever read off a rack in a general store in Satsuma, Florida.

In Barrier Island, MacDonald comes back to issues he explored in A Flash of Green, but that book was of its time and this one is of now, which makes it very worth reading. In this book, there are no clear winners, nor clear losers, although quick there are, and dead. There are only deals and those privy to them, and everything else is more or less subsumed in the great god, Transaction. There is no escaping a world so constructed and centered, not even for Wade Rowley, who is trying to steer a decent course between essentially opposed value systems.

MacDonald has for some time been coming to grips with the utter commercial debasement of a world he knew in better times than these. It's a good and worthwhile subject, but it's awfully close to the marrow. In Barrier Island, it seems to me that MacDonald's found the voice and format he's been looking for, and given us both a good story and -- at least for the reader who gives a damn about the way the world works -- some bitter food for thought about a culture which values itself in terms of real estate.