FOR Hubert de Givenchy, putting the final touches on his exhibition in Washington was like getting together with old friends. "Jacqueline Onassis sent me a note after she wore this white gown to dinner at Versailles with President de Gaulle," said the towering designer as he adjusted a long white coat on a mannequin at the Departmental Auditorium this week. There had been some raised eyebrows about the possibility of the former first lady wearing a French designer gown in Paris, but the next day Onassis sent Givenchy a note with a simple line drawing saying, "President de Gaulle said I looked like a Watteau last night."

Onassis sent the original of that gown to the Kennedy Library in Boston, so Givenchy recreated it for this 30-year retrospective show. But others are the originals, just as Givenchy's clients and friends wore them, minus their personal jewels, of course. The black, double-breasted coat Givenchy made for the Duchess of Windsor to wear at her husband's funeral is displayed without the black veil . . . or the lavish necklace she wore.

Next to the Onassis costume is the gown Givenchy designed for Babe Paley, given back to the designer for his collection by Bill Paley after his wife died. The embroidered fabric with touches of pailletes looks like a Flemish painting. The paintings of Miro', Braque and de Stael clearly influenced a group of gowns naearby made for Bunny Mellon.

The best-known dress of the collection is a black cloque' scoop-neck style Audrey Hepburn wore in "Breakfast at Tiffany's." But there are several others from Hepburn's personal closet, including a bias-cut, black satin gown ingeniously cut to trace the figure and bare the back.

Also not to be missed: The first party dress worn by Princess Caroline of Monaco; a navy blue chemise from Givenchy's first collection 30 years ago and a similar one from last year; an embroidered suede djellabah made for Madame Schlumberger, and the Fortuny-inspired panne velvet and embroidered dresses. The clothes are all from Givenchy's couture collection, a breed of clothes rarely seen in Washington and never in such quantity.

The exhibition, sponsored by Garfinckel's, opens to the public tomorrow and continues through Feb. 25 at the Departmental Auditorium (1310 Constitution Ave. NW.). Few cities have a show with such richness of design and fabric; it should be required for students of fashion, those who sew and those who simply care about clothes. (Regrettably, the exhibit is closed weekends.)

Givenchy, who designed the Tower Suites for the Vista International hotel, will be back in Washington in a week to be honored at lunch at the French Embassy and dinner with his friend and client, Deeda Blair. (Two Givenchy designs for Blair are in the exhibit.) A gala dinner Feb. 22 will benefit the National Museum of Women's Art. (The dinner is underwritten by Sandoz Inc., a Swiss-based pharmaceutical company that supplies the dyes for the most of the textile companies around the world.) The retrospective, which was first seen in New York at the Fashion Institute of Technology, will be sent to Tokyo and Osaka. The Washington show is half the size of the original New York show, but clearly the better half, and the setting is far more impressive. "It makes us seem terribly rich," said fashion illustrator Joe Eula, who came to Washington to make sketches for the show.

"The Winds of War" blew a great opportunity as a showcase for fashion. There were some signs of the early 1940s, like the back-zip dresses, hats that match dresses, full slips and Robert Mitchum's polo coat. But for the most part, it was a mix that missed the very obvious '40s themes that are currently being revived and reworked by New York and Paris designers.

The Metropolitan Museum of Art will showcase the 25 years of Yves Saint Laurent's career for its next major fashion exhibition. The current show, "La Belle Epoque," has proved to be one of the most popular of the 11 shows organized by Diana Vreeland, special consultant to the Costume Institute at the Met. It has been seen by 178,000 people since it opened Dec. 21.

Washington model Gloria Burgess came home this week, but very briefly. Burgess, who lives in Paris, waso on her way from the Paris couture shows to Palm Beach, Fla., where she was modeling for Japanese designer Hanae Mori. Two days later she was off to Japan to model in several collections, and by late February she expects to be in Milan and Paris for the ready-to-collections.

What does a top model, who has access to all the best clothes in the world, choose to wear? When she stopped by this week, she was wearing a black YSL sweater she's owned for five years, a long, black wool circle skirt from Claude Montana that she bought last year, last season's boots and a huge challis shawl from Christian Dior. "The only thing I've bought recently were two dresses from the couture at Dior," said Burgess. "They were fitted on me so they never sold, and I bought them off the sale rack."

Burgess makes it a rule to travel with only one suitcase. "I find I am comfortable wearing the same things most days, changing only the sweater." Almost everything she has is black. "It is like having a wardrobe of movable parts."

Joining the ranks of the rich and famous who have turned a preoccupation with clothes into an occupation is Vicomtesse Jacqueline de Ribes. Like Carolina Herrerra, Betsy Bloomingdale, Charlotte Ford and Gloria Vanderbilt, de Ribes will shortly have her own label, putting the talent she has for choosing clothes--that has put her on best-dressed lists umpteen times--to designing clothes. The clothes will be strictly for cocktail and evening wear, made in France but sold only in America. A longtime friend and client of Saint Laurent (and more recently Emanuel Ungaro), she will only have to check her own closet for a fabulous range of ideas for her collection.

Yves Saint Laurent has found a new way, and an old one, to hang jewelry on his models. In recent couture showings, he added jewelry to a low-back dress by putting a glittery belt around the waist under the dress which showed through the de'colletage. He also bowed to the 1950s with the ankle bracelet; his, more glitzy than those 30 years ago.

Alain Chetrit, the owner of Silhouette Boutique in Georgetown, goes regularly to the mens wear fashion collections in Europe to spot trends. Last week he came back from Italy with some fresh ideas--fuller, pegged pants, big sweaters and colorful shirts. The shirts, it turns out, are his own design, and stores around the country were buying the them right off his back. Chetrit designed the first bicolor shirt with a collarless snap front for himself, in several combinations, including black and yellow, white and green, taupe and black. He now has 13 different styles. To date, he has sold 2,700 shirts to stores including Barneys and Suzuya in New York, and Ultimo in Chicago. They are at Silhouette, too, of course.

Sometimes designers wish their clothes weren't so appealing. Harriet Winter had just moved into her new showroom loft on West. 25th Street in New York when burglars broke through the brick wall in a stairwell and took her latest samples. "They were very selective," said Winter. "For every skirt they took a jacket, for every blouse at least a skirt or pants."

Woodies' young designer salute on March 3 should provide a boost to other young designer hopefuls. The store will initiate scholarships in the name of Lloyd Allen, Hino & Malee and D.D. Dominick at the Fashion Institute of Technology in New York. Some may be marked for Washington-area students.