For a few hours last night, in the high-vaulted, Victorian grand hall on the third floor of the National Portrait Gallery, it was almost as though the Jazz Age had not died of acute depression half a century ago. Nowhere on the premises was there a bathtub full of illicit gin, but the champagne was abundant, there were reliable reports of a flask in at least one hip pocket, and couples were frenziedly dancing the Charleston in knee-jerk reaction to a period jazz combo called Hot Mustard.

The party was held to celebrate the opening of the Gallery's new exhibition: "Zelda and Scott: The Beautiful and Dammed," which sat quietly one floor below the 550 dancing, tippling and celebrants, visited by little knots of Fitzgerald fans between bouts of partying. "Look, that's us," said one old couple who had been young in the '20s, standing before a painting of people on a beach in the knee-length bathing suits that were considered daring at the time.

Upstairs, an energetic effort was being made to recreate the spirit of the age, and minus a touch of decadence, a sense of dancing on the edge of the volcano, a fair approximation was reached. "I think it must have been exactly like this," said Scottie Fitzgerald Smith, daughter of the beautiful, ect., couple, who was a very young child when the Jazz Age (given that name by her father) was alive.

"Some of those Charleston dancers are almost professional," she said glancing at the hectic gyrations on the dance floor. "I can't imagine where they learn to dance like that today. Surely you can't Charleston in a disco."

The secene looked remarkabley like a John Held cartoon brought to life. Some guests chose the optional black scene, but a majority chose the more colorful option, "Jazz Age Costume," offered on their invitations. There were many short dresses and long chains of pearls, feather boas and cloche hats, headbands and ostirich feathers that summoned up the spirit of Theda Bara.

One woman wore a vintage tea gown with a little, flat white hat. There were a walking stick with a silver knob, several very long cigarette holders, white flannels, a few spats, plus-fours (with argyle stockings), and a variety of brightly colored sports jackets tending to outrageous shades of red or orange. Many of the gentlemen were wearing hats on the dance floor -- a practice that would hardly have been permitted in a reputable dance hall 50-odd years ago. But they were part of the costume and would have done nobody any good sitting unseen in the check room. There were cloths caps with buttons on the top, a variety of straw hats, and even a few black fedoras that looked slightly out-of-period. There was also, inexplicably, one pith helmet.

"This is the fulfillment of a fantasy," said Sandra Westin, of the Gallery staff, who had made many of the arrangements for the party. "Back in 1950-something, in college, when I was reading F. Scott Fitzgerald, I used to dream about what it must have been like and I wanted to make it happen again. When they began talking about plans for this exhibit, I told them, 'Look, you're crazy if you keep this thing small. This is everybody's fantasy life you're dealing with.' All these people came here tonight to make my fantasy -- and their own -- come true."

There was, in fact, a lot of role-playing -- people standing in the slightly angular postures familiar from cartoons of the period and, late in the evening, sitting on the marble steps leading up to the chairless dance floor in the kind of positions flappers and their beau have in the old pictures. everybody seemed to think it was perfectly natural to put on the total style with the clothes, and occasionally a "cat's meow" or "23 skiddoo" would emerge clearly from the dance-floor hubbub.

Scottie, surrounded by a throng of her friends and her parents' admirers, spent much of the evening parrying questions. "No, I spend most of my time in Montgomery, now. . . Well, I had a feather, but I gave it to my daughter; she looks so much better in it. I think you have to be under 30 to wear them well. . . Yes, that Mediterranean villa he mentions in"Tender Is the Night' is still in its orginal condition. It's on the market right now, and I'd buy it if I had $1.3 million."

Her contribution to the exhibition included some of her mother's paintings, which usually hang in her home in Montgomery, Ala., where Zelda was a belle and an aspring ballerina 65 years ago.

She remembers being a little girl with these extraordinary parents and taking it for granted: "I thought that kind of life was just normal and average for little girls."

One item in the exhibit is a set of paper dolls of Scott Zelda and Scottie that her mother made for her when she was a child. "I think perhaps her best paintings were her paper dolls," Scottie remembers. "She made me the whole court of Louis XIV and all the fairy tales: Little Red Riding Hood, The Three Bears, Alice in Wonderland and King Arthur's Court."

What she did not consider normal was the way she got her allowance later when she was at Vassar.

"He used to send me $13.50 per week, and everybody else go their allowances once a month. There would be a letter with each allowance, and it would be full of advice. I think that may be why he sent it once a week, because he liked to give advice, but young people don't like to receive it. I would just open the envelope, take out the allowance and put the letter in the drawer without reading it."

Now, those unread letters are colletors' items, one of them is on exhibition in the National Portrait Gallery, and they are worth a lot more than the $13.50 that used to be the reason for opening the envelope.