MIAMI By Joan Didion Simon and Schuster. 238 pp. $17.95 GOING TO MIAMI Exiles, Tourists, and Refugees in the New America By David Rieff Little, Brown. 230 pp. $16.95

ON VARIOUS occasions over the years, Joan Didion has claimed that she isn't an intellectual, that she can't think in abstracts, and that she hasn't any talent for some of the standard procedures of journalism such as interviewing.

I have always found these notions curious, and perhaps a bit disingenuous, because Didion's writing so thoroughly belies them. In book after book, essay after essay, in fiction as well as nonfiction, she writes and thinks with exceptional rigor and originality, makes connections both abstract and specific with skill and grace, and brilliantly marshals masses of detail, much of which she obviously gathered in interviews. Notwithstanding her self-deprecatory remarks, therefore, Joan Didion for me is an intellectual of a high order and one of the preeminent journalists of our time.

As evidence for the unconvinced, one need cite only a few examples. There is the essay on Hollywood in The White Album that guts the conventional wisdom about the workings of the motion picture industry. There is the portrait of Jack Lovett in the novel Democracy, which so accurately captures (without stereotyping) a certain breed of shadowy quasi-governmental American operative in the Pacific during the Vietnam period. And of course there is the accumulation of writing, through more than two decades, about the places of the Pacific -- California, Hawaii, Central America, Mexico -- that constitute perhaps the most evocative and insightful body of regional reportage ever published in English.

Now there is Miami, Joan Didion's most ambitious nonfiction work yet.

Among the things Didion does in Miami: she profiles South Florida, the most complex metropolitan area in the United States and the only one without a center of gravity; she probes the psychology of the huge, accomplished, and multifarious Cuban exile community (56 percent of Miami proper is Latin and 43 percent of Dade County), whose attitudes and intentions are rarely what its Anglo neighbors and Washington manipulators think they are; she analyzes United States policy toward Latin America -- Cuba and Central America in particular -- during the last six American presidencies, from Kennedy and Allen Dulles to Reagan, William Casey and Oliver North, from the 2506 Brigade at the Bay of Pigs to the contras in Nicaragua, and poses chilling questions about Washington's repeated betrayals, or perceived betrayals, of its Cuban and other Latin allies, about the White House's arrogant toying with Latin policy over nearly three decades, and about the lethal consequences "on the ground" in Miami.

Having covered all of that and more, Didion probably will be accused of writing too much based on flimsy reporting (she apparently spent only a few weeks in Miami and Washington), just as she was criticized for writing at length on El Salvador (Salvador) after only two weeks in that country. Such criticism is fallacious. Didion doesn't pretend to do more research that she does. She tells us exactly what we are getting. And Didion's reporting for these books wasn't limited to her time observing and interviewing in El Salvador, Miami and Washington. She has done extensive and well-focused documentary research as well, reflected in an informative chapter-by-chapter source appendix at the end of Miami.

Further, and most important, Didion thinks about her research with a brutal discipline that is unique. Anyone can do research; no one else thinks and writes like Joan Didion.

Far from writing too much in Miami, Didion actually writes with a severe economy (a characteristic of her work from its beginnings), and it is that economy in part that makes Miami by far the best of the recent books published on this subject.

IT IS easy to overwrite Miami. The city is so unrelievedly hot in nearly every sense, so volatile, so symbolic, so contradictory, with so many extremes and strong stereotypes, that an author must approach it with extra caution. Without a tight rein, adjectives and adverbs pile up quickly. Prose becomes shrill. The truth about Miami is more likely to emerge from a relatively few calm words than from the jambalaya of verbiage that the subject, on the surface, seems to invite.

"Havana vanities come to dust in Miami" is the simple, quiet sentence that opens Didion's book and defines everything that follows, bearing the weight of 2XX pages in perfect balance. "Havana," in this opening sentence, is not only the capital of Cuba (and of exile Miami) but the focus, at least metaphorically, of a multitude of adventures that Cuban leaders have initiated over several decades and that American presidents have perpetrated in Cuba, purportedly on behalf of Cuba (or certain Cubans) or other Latin countries (or certain of their citizens.) The "vanities" of "Havana vanities" encompass these adventures and other flings of policy, usually involving American arrogance and misplaced Latin expectations and dashed hopes. "Come to dust" here refers not only to the general disintegration and failure of both Cuban and U.S. initiatives such as the Bay of Pigs, but also to the fact that a number of deceased Cuban leaders (and thousands of followers), together with Somoza of Nicaragua, happen to be buried in Miami, which, in this opening sentence, isn't just a city in South Florida where hundreds of thousands of Cuban exiles live in awkward proximity to a roughly equal number of Anglos. Miami is the dumping ground for the eruptive human "residue" -- the "disposal problem" in Washington's terms -- of all that has gone wrong between the United States and its Caribbean and Central American neighbors in this century. "Havana vanities come to dust in Miami" is one of those rare first sentences whose power stops the reader, as if there were nothing more to say, and then propels him, eager to experience the author's elaboration.

Despite its potent political analysis, Miami is not only, or even primarily, a political book. It doesn't take sides politically in the current Nicaraguan conflict, for example. Didion's concern is more sociological and psychological -- the psychology of national betrayal and its consequences. Miami, moreover, is Joan Didion's personal portrait of a singular place in our world, a place where she employs many of her familiar bench marks: commerce and real estate ("The feel was that of a Latin capital, a year of two away from a new government. Space in shopping malls was unrented, or rented to the wrong tenants. There were too many shoe stores for an American city . . . Local money tended to move on hydraulic verbs: when it was not being washed it was being diverted, or channeled through Mexico, or turned off in Washington."); weather ("There were rains so hard that windshield wipers stopped working and cars got swamped and stalled on I-95. There was water rolling and bubbling over the underwater lights in decorative pools. There was water sluicing off the six-story canted window at the Omni, a hotel from which it is possible to see, in the Third World way, both the slums of Overtown and those island houses with the Unusual Security and Ready Access to the Ocean, equally wet."); social rituals ("Almost any day it was possible to drive past the limestone arches and fountains which marked the boundaries of Coral Gables and see little girls photographed in the tiaras and ruffled hoop skirts and maribou-trimmed illusion capes they would wear at their quinces, the elaborate fifteenth-birthday parties at which the {Cuban} community's female children came of official age. The favored facial expression for a quince photograph was a classic smolder. The favored backdrop was one suggesting Castilian grandeur, which was how the Coral Gables arches happened to figure . . .").

Although Joan Didion sets the highest standards of prose, and meets them through much of Miami, she occasionally falters. Miami is not as well written as Salvador. Some of her sentences are far too long, needlessly so, uncharacteristic of Didion. And for my taste she starts too many sentences with substantive clauses beginning with "that." ("That these were the men in black tie who now danced with the women in the Chanel and Valentino evening gowns on the ballroom level of the Omni was an irony lost in its precise detail . . . "). The substantive "that" clause, popular in academic writing, is rarely the smoothest way to begin a sentence. However, these are only quibbles about a brilliant book.

DAVID RIEFF's writing is as undisciplined as Joan Didion's is controlled. Rieff's Going to Miami begins with a vexing author's note. In "a number" of instances through the book, Rieff tells us, he disguises "real names and stories" and "conflates" incidents, either because of "the literary requirements of my text or a desire not to embarrass people who became my friends. This is a book of impressions, not a work of investigative journalism."

Rieff does not define his literary requirements, or his literary intentions for that matter, and they do not become evident as one reads his book. So we are left with his "disguises," his "conflations," and his "impressions." Since his disguises and conflations by their nature are concealed, it is difficult to comment on them, except to express discomfort with such devices in nonfiction. As for Rieff's impressions, it is my opinion, based on two years of living and reporting in Miami, that many of them are superficial and ill-founded.

Rieff clearly believes in exaggerating to make his often dubious points. When one reads that "Don Johnson was on the cover of every magazine in America," or that Coconut Grove is "one vast condominium," or -- more important -- that Anglo dislike of Cubans is "hysterical" and "desperate," or that the "survivors of Brigade 2506 were paraded gleefully on Cuban television, but, with a few exceptions, there were no atrocities," one must conclude that the author is a stranger to precision and prone to inflation and febrility. When Rieff writes that "with a few exceptions, there were no atrocities," it is like saying that with a few exceptions, there were no bombs in the crowded building." The exceptions kill people -- and atrocities perpetrated by the Castro government killed members of the 2506 Brigade. To flick them aside as "exceptions" without elaboration is warped and reckless reporting.

When an author consciously exaggerates, he often unconsciously commits bald errors of fact, however minor, and Rieff does not escape. One example: Fulgencio Batista did not live in Daytona Beach "during the late nineteen-thirties, after his first stint as Cuba's president," as Rieff writes. Batista governed Cuba from 1934 to 1944 (with the title of president during the last four of those years). He then lived in Daytona Beach, among other places, until he returned to Cuba and seized control again in the early 1950s.

(In fairness, one must also point out a rare factual error in the Didion book. She writes that in 1961, Playa Giron, a beach at the mouth of the Bay of Pigs, was on the southern coast of Matanzas Province. In fact, the province was Las Villas at that time; Matanzas Province didn't include Playa Giron and the Bay of Pigs until many years later when Castro redrew provincial boundaries throughout Cuba. A small slip, to be sure, but it appears in the first few pages of the book and will at least mildly irritate Didion's potentially huge Cuban readership.)

If David Rieff appears unlucky to have his book published simultaneously with a far superior book by Joan Didion on the same subject, it could have been worse. Rieff could have been published alone, and therefore subjected to closer and more detailed scrutiny.

David McClintick, the author of "Indecent Exposure: A True Story of Hollywood and Wall Street," has lived in Miami for the past two years while researching a book on federal law enforcement.