Horse-drawn carriages with drivers in top hats were parked along Fifth Avenue outside the Metropolitan Museum. Inside, in the grand foyer of the museum, lit by mock gas lanterns, young girls in bustles and trains strolled with men in knickers and caps. It was the Belle Epoque revisited.

The glitterati, a mix of fashion royalty and socialites, movie stars and merchants, put on their sequins and satins, velvets and lace, to salute the new costume exhibition at the Met, La Belle Epoque.

Marcel Proust couldn't have plotted a better setting.

He would have approved of the guest list, too. Betty Ford in black velvet and fox, with designer Albert Capraro. Raquel Welch in a second skin of leopard-printed sequins, with husband Andre Weinfeld, and Pierre Cardin with Lynn Wyatt, in a Cardin pleated creation. Cristina Ferrare showed up with Halston, and Dior's designer, Marc Bohan, at one moment had Nancy Kissinger on one arm and Nan Kempner on the other, both in the same black and white Yves Saint Laurent. "I didn't do it! I didn't do it!" Bohan said gleefully to the crowd of paparazzi.

"This is the most dress-up moment of the year. You dress for the museum and for Diana [Vreeland] and for the season," said Betsy Bloomingdale, who arrived with Jerry Zipkin. She was wearing a satin strapless gown by Dior; she had to check with Zipkin to get the designer's name.

This splashy event, not unlike a grand night at Maxim's in turn-of-the-century Paris, was held for the 750 guests who paid $500 each to get a sneak peek at Vreeland's 11th annual costume show and to dine in a setting recreating the original Paris Maxim's on a dinner of coquille Saint-Jacques and cold fillet of beef filled with pa te' de foie gras. They dined on tablecloths of pink starched linen topped by small lamps with pink silk shades -- all just like the original Maxim's.

That was the point, of course. Pierre Cardin, sponsor of the exhibition and owner of the Paris restaurant and all of its spinoffs, had recreated Maxim's for the evening.

The Belle Epoque, the era when the rich and titled indulged in conspicuous consumption and wealth and power meant little if you didn't dress the part, is the theme of the new costume exhibit, which opens to the public Dec. 21 for 10 months at the Metropolitan.

For Vreeland, special consultant to the Costume Institute of the Met, it is her most splendid show.

The rich varnished wood paneling, beveled mirrors and elaborate light fixtures that have surrounded diners at Maxim's since the turn of the century help showcase the exhibit. (The tickets for the opening to benefit the Costume Institute were sold out even before the formal invitation got into the mail.) After dinner between 1,500 and 2,000 more guests paid $100 each to see the costume exhibit, ogle the dinner guests and dance in the Temple of Dendur to the music of Lester Lanin's Orchestra.

"Of course I loved this period, I was born in the middle of it," said Vreeland, who recalled "playing in the Bois [de Boulogne], rolling hoops and that sort of thing."

Cardin who is scouting a location for a Maxim's in New York, is reported to have spent more than half a million dollars to sponsor the exhibition and create the dinner setting. Ever the gallant Frenchman, he says it gives him a chance to thank America for the 25 years he has done business here. But ever the businessman, Cardin can use the 20 tons of decor, shipped here by air in 48 huge cases, in future Maxim's restaurants, one already planned in South America, and four others in the United States, including possibly one in Washington.

The clothes of the exhibit document the three shapes of fashion that evolved from 1890 to pre-World War I and include dresses that were in the closets of some of the most dashing women of the time, including Mrs. Andrew Carnegie and Mrs. Cornelius Vanderbilt; Comtesse Greffulhe, who was the inspiration for Marcel Proust's Princesse de Guermantes; Lily Langtry, and one who was not so dashing but was quite influential, Queen Victoria.

The Victorian period is apparent in the boned bodice gowns, and the huge sleeves that emphasize the hourglass figure. Even the fabrics were rigid in this period; the stiff Jacquard silks and satins are garnished with braids and ribbons and laces tacked into place.

In the Edwardian period the ideal was a far more mature, full-blown woman with a pigeon monobosom; her clothes were all in soft fabrics such as chiffon, gussied up with tucking, applique' and ribbons. It was the ultimate in ostentatious fashion. Charles Worth, the Bill Blass of that time and place, designed some of the best of the sumptuous clothes that are on display.

The final period, post-Edwardian and pre-World War I, is distinctly different from the two other periods, with clear signs of a modern woman emerging. She is dressed to be out on the streets, in narrow skirted suits and sensible shoes. It was the appearance of Diaghilev's Ballet Russe in Paris that most dramatically rocked the times. The limber bodies of the dancers, free of corsetry, and the vibrantly colored Oriental costumes made women unhappy with the old style and anxious to break into the kind of revealing clothes designed by Paul Poiret, for example. "It brought about a lot of confusion with women ready for a change but not sure how to interpret it," said Stella Blum, curator of costume at the Metropolitan Museum of Art.

To get the plumper figure that was the style of this period, mannequins had to be fleshed out with cotton padding, said Blum, pointing to the ample thighs obvious beneath one of the slim dresses. Even the Poiret beaded dress with tassel in front, remarkably like an Erte' drawing, had to be padded through the middle to look right on the mannequins.

The lighting seems more appropriate for a dinner at Maxim's than a display at a museum, but that's done, as usual, to preserve the clothes that will be on exhibit. "It also helps not to show off their tiredness," admitted Blum, who said some of the clothes look that way simply because they are old.

In spite of the dim lighting it is possible to see the remarkable restoration done by the museum staff and volunteers. Some of the dresses needed only to be refreshed enough "to take the closet look" out of the clothes, but others needed a more dramatic boost. A black sequined dress by Callot Soeurs had so many bald spots, said Blum, it took one volunteer four months to put back the beads.

One of Queen Alexandra's dresses was so fragile "I touched it and it snowed sequins," said Blum. More than 50,000 new sequins were attached to get it back into shape.

Vreeland's shows have always had a strong impact on contemporary designers all around the world -- not only the clothes themselves, but the way they are displayed.

And by the end of the evening many designers were plotting to restore sequins and glitz and other signs of luxury to their next collection. "I think everyone is tired of jeans and dressing down," said Adele Simpson. "You need clothes to put a bit of fun in your life."

James Galanos says his customers, Nancy Reagan among them, "want the elegance that's been missing in the past few years." Said Geraldine Stutz, who is president of Henri Bendel, "Just look around, the period of luxury is already here."