Art Deco has planted its jaunty flag on the beachhead of Florida developerism.

The style, all the rage half a century ago, is blooming again in the square-mle historic district of South Miami Beach.

And in the heart of that district last weekend, seven small hotels owned and restored by the Art Deco Development Corp. were bursting with excited young people dressed in 1939 New York World's Fair shirts, clinging '30s dresses, berets, cloches, straw hats, black bow ties and in fact any style from '20s to '50s.

They were everywhere -- running in and out of futuristic facades, lounging in sleek neon bars with terrazzo floors, sipping martinis from classic inverted-cone glasses, squirting fizz from vintage seltzer bottles, jitterbugging and black-bottoming on the street to a wild variety of music from Glenn Miller sounds to the roaring old trombone blat of the Bourbon St. Jazz Band.

In an amazing three-day orgy of films, lectures, tours, concerts, fashion shows, antique auto displays and bazaars attended by at least 70,000 people (say the backers), the fifth annual Art Deco Weekend drew fans from all over the country and Europe, notably design-conscious Holland and Sweden.

It also seemed, and not by accident, to impress some of the city council members who up to now have been most reluctant to get involved in a restoration project that stood in the way of ever-more, ever-taller high-rises along South Miami Beach's newly resanded $64 million ocean front.

What is Art Deco anyway?

As the name implies, it is not functional, not architectural, not a formal building style at all. It is a look.It combines smooth, fat curves with the straight lines of the machine age. Its shapes are simple and unsubtle. Its colors are strong and definite, always used in dramatic contrast: black and silver, maroon and gray, mauve and taupe, sea blue and white. There is a Flash Gordon touch in the swooping vanes attached to a building top to make it a space ship rammed into the sand. It is not quite camp: The camp came later, in the '50s, when -- deteriorating to rococo excess as every style eventually does -- it became Art Decoco.

The style came out at the International Exposition of Modern Decorative and Industrial Art in Paris, 1925. Born in the Modern movement that first stirred in Parish, Vienna and Munich at the turn of the century, it grew up in a sort of love-hate relationship to Art Nouveau, cubisn, de Stijl and Bauhaus, adding hints of African, Mayan, Egyptian, Moorish, Japanese and American Indian styles, plus assorted exotica: Diaghilev, Braque, Matisse, Fred Astaire, borzois, flamingoes, zebras, orchids, seashells and lightning bolts, all done in ivory, ebony, mother-of-pearl, etched glass, crystal, marble, Florida's decadently ravaged-looking keystone coral, celluloid or other novelty plastics of the '20s. It was a style made for plastics.

In a word, if there is a word, Art Deco is eclectic.

Maligned in recent decades as vulgar and gimcrack, it has suddenly taken on new dignity. Luckily, being a fun style, is makes friends easily. And surely the best friend it ever had in Miami Beach -- next to New York and Los Angeles the country's greatest Art Deco treasureland -- is a 61-year-old hurricane named Barbara Baer Caitman.

Day and night, she lives Art Deco: in her apartment in one of the historic district's 800 Deco buildins, in her post as president of the Miami Desin Preservation League, up and down the two-block midway on Ocean Drive last weekend, where she was approached about twice a minute for six hours by people needing this or that. She has been called, in print, "the mother of us all," and her express-train energy has earned her some other names, too.

"This is the most corrupt city I ever saw," says the Chicago-born ex-New Yorker. "It's so venal. When we started in '76 the developers were working their way down from North Miami Beach. This area was in bad shape, the good decor had been taken away, they told us we couldn't restore it because it was all built with beach snad and couldn't last two years. This was not true. It was one of the rumors wer fought."

Her husband, William, a New York architectural critic and editor, had died the year before, and Capitman, an art historian (NYU and Pittsburgh), wanted to keep busy.She decided to look for alternatives to the mindless growth, the conspicuous consumption that she say around her.

"We announced a meeting on preserving the Art Deco buildings here. I didn't know there was such a passion for it: We drew 400 architects and designers. Well, we decided to stretch their minds. We put on 20 speakers and kept going until 1 a.m."

Next came a survey and a campaign to establish a national historic district. After a bitter four-year struggle (the developers called their project "a cancer," among other things), they won for Miami Beach the nation's second larest district, after New Orleans. But that was just the opening salvo in a battle that still rages over this lively 20-block stretch of gleaming white plaster shops, apartment houses, hotels and bungalows.

In 1979 Capitman's Groton-educated son, Andrew, and his partner, Mark Shantzis, still in their 20s, bought the 70-room 1939 Cardozo Hotel for $800,000. Today their Art Deco Hotels Ltd., consisting of more than 100 investors from almost everywhere except Miami Beach, has put $11 million into seven hotels with a total of 452 rooms.

The restoration work has attracted talent from all over, which in turn has generated two new restaurants, an exclusively Art Deco store and a booming market in almost-antiques. Last weekend a bustling bazaar was set up in a row of tents that completely blocked out the sea view -- somewhate self-defeating at a beach resort, one might think.

But the point is, these hotels are small. They are human scale. They have one elevator and a registration desk the size of a walk-in closet and a homey lobby. The tallest building for miles is The Tides, whose original name was The Skyscraper. It is 10 stories high.

Developers working their way south from the Gold Coast and its monster hotels (the Fountainebleau Hilton alone has 1,200 rooms) want to erect a 33-story tower where the White House Hotel burned down last summer. Builder Abe Resnick tore down the neat little New Yorker two years ago, and the Deco people are worriedly watching the vacant site. In a city where land values count far more heavily than building values, the question is whether the historic-district designation can actually stop big-time builders in or out of Miami Beach's billion-dollar redevelopment plan. Construction totaled $150 million in 1980, tripled from the year before.

Demonstrating what one opponent called "their 1960s mentality," the city council enacted for the Deco district a preservation ordinance that required 100 percent of the property owners' approval, effectively negating the whole thing (51 percent is normal). But the Dade County attorney rejected the ordinance as "an improper delegation of authority." Today the Metro Dade Preservation Commission has charge of the situation pending a new ordinance. If a strong ruling is not enacted soon, the Deco group plans to sue.

One developer, Ronald S. Molko, is smitten with Art Deco and is warily accepted as a possibly ally.

"I'm not a preservationist, I'm a businessman," he says, "but I feel the Deco area will do for Miami Beach what the Village did for New York.

It offers a lot to the future of the city, getting young intellectuals in here."

He echoes Andrew Capitman, who wishes the city would stop trying to be another Las Vegas and instead make the most of its unique charm, like Nantucket or Georgetown.

Whatever happens, the old people who have lived in the Deco area for decades apparently are expected to disappear from the scene. Their dominance is fading fast: In 1970 they made up 90 percent of the population; now it is down to 50. The kosher butchers, pastrami restaurants and Judaic art supply dealers are being replaced by Cubans and Haitians, and now also by the apostles of Art Deco.

This week, taking adventage of the considerable tax break that comes with a historic district, Molko opened his $1.5 million '30s Promenade shopping plaza, restoring a 1941 building on Washington Avenue, two block west of the beach. Interior design was by Leonard L. Horowitz, a founder with Barbara Capitman of the preservation league. It was Horowitz who created a palette for 40 colors to be used in a city-funded 12-block revitalization project for the avenue.

"I'd like to have everything in the block be in values of one color, which would then be the trim color in the next block," he says. "These are natural colors, sunrise and sunset colors, sand and ocean colors. I love the Eyptian tomb paintings, too. These colors have energy. When you put them together they bring out different depths. You can't learn it, you just know. Myself, I work on vibrations." They are Benjamin Moore colors, by the way.

Recently, Horowitz and Capitamn toured the country for three months searching for Art Deco, and last week Capitamn, as president of the Art Deco Societies of America, gave awards honoring Deco activists and 10 top Deco buildings. These include in the Washington area the Shoreham Hotel with its restored Marquee Lounge and the Greenbelt Elementary School.

About those activists: There aree a bunch of them, and they are ready to fight City Hall. It has been pointed out that the Capitamn group is after all financially interested in the local success of Deco. But many others with nothing to gain have spared no expense to bring back the look.

A casual visit to some homes in the area turns up breezy fantasies of black-and-white tile, rippling glass brick, blue mirror clocks, teapots shaped like diners, chrome-plated cocktail shakers, sleekly curving black enamel bars, moon gates and, in one case a lovely covered sort-of-Moorish balcony that helped transform a 40-year-old $6,400 bungalow into a $150,000 showplace.

The irony is almost too neat: Miami Beach had its first great boom in the middle of the Depression. That was when much of the Art Deco first appeared here. Now hard times are upon us again -- and look what's coming back.