Andre'e Putman loves a challenge. The tall, striking woman, creator of the Yves Saint Laurent Rive Gauche boutique in the Watergate, is leaning against one of the two marble columns in the center of the shop. A third pillar is in the distance behind her. "This shop was biscornu--had wrong corners."

"This space was so difficult, all odd shapes with one terrible column in the center," Putman explained on a brief stop in Washington recently to check the progress of her most recent project. Rather than hide the column she made it thicker and enclosed it in white marble, added another to make a pair, and added a third column "for balance" at the back of the store.

She has turned the challenge into the stunning focal point for Washington's most attractive new shop, one of several boutiques she has done in several cities for the Paris designer. Last night a stylish crowd turned out for the opening and to meet Pierre Berge, Saint Laurent's business partner.

"I've come to take care of Marlene; she goes on all my trips with me," said Special Ambassador to Central America Richard Stone, speaking of his wife.

"I wanted to show my husband Gil the shop he helped pay for," teased Margot Hahn, who was comparing the prices of the items she bought in the Saint Laurent Boutique in Paris with those on the racks in the Watergate. "Margot changed the balance of payments single-handedly," said attorney Gil Hahn.

Putman can claim the ultimate design credit: She is the favorite designer to the most important French designers. Along with the shops for YSL, she has done apartments for Chloe' designer Karl Lagerfeld in Monte Carlo and Rome, and residences, offices and boutiques for Thierry Mugler, Claude Montana and Azzedine Alaia. Coming up is a small hotel, as yet unnamed, in the Murray Hill section of New York.

Although she is often pegged as super-trendy, Putman insists that the biggest compliment she receives is when her work proves to be a classic that lasts a long time. "I don't like to do things ultra-trendy. They die. And, like punishment, they reappear," she says in her deep, throaty voice. "When people say to me, you did my house 20 years ago and people think I had it done last week . . ." She doesn't finish the sentence but it is clear she is satisfied that that is a job well done.

She prefers to be called an interior designer rather than a decorator. Capitalizing on space and light, she has done the YSL boutique in white, black and gray. "I am not interested in being amusing with color. Flowers, people and paintings bring color." As if to prove the point, she stops as Sally Marx, who owns and runs the boutique, passes by in a brightly printed skirt.

She is partial to black and white for her own wardrobe. On her visit to Washington she was wearing a white silk knit dress by Alaia, but she often dresses in black. In fact, at last night's party she was wearing a new black coatdress by Saint Laurent. "I never thought black was sad. It is like a box made to hold a jewel," she says. "It is always black. Black is the base for everything." In Japan, she has designed a Chinese restaurant all in black.

Black is used for the cases and mannequins, which look like Brancusi sculptures, in the new boutique, and in the center of the steel-gray carpet is a trompe l'oeil rug of white and black marble. "You need a rug to walk on," she says, "but wall-to-wall rug . . . that is boring." She likes things that are trompe l'oeil; her new sheet collection for Wamsutta looks wrinkled and quilted--but it is neither, it is part of the pattern. "Trompe l'oeil has charm. It's amusing," she added.

Absence of color is not a new idea for Putman. In the mid-1960s, when she was a design consultant for Prisunic, the French equivalent of a five-and-dime, she introduced all-white plates. (She also persuaded the store to sell original lithographs by several artists, including Alechinsky and Niki de Saint Phalle). In the early 1970s, she was the director of "Cre'ateurs et Industrie," a group that first showed the clothes of designers Jean Muir, Jean-Charles de Castelbajac, Issey Miyake and others. The show took place in the courtyard of the Bourse, the French stock exchange, and most of the clothes were black.

If she was too early with those designers, her timing is on target with the pieces of furniture she reproduces from such 20th century artists and designers as Mariano Fortuny (well-known for his pleated dresses but not his furnishings), Eileen Gray and Michel Duffet. Her first business with Saint Laurent was his purchase of her reproductions. Saint Laurent likes the spare dining room chair by French architect Robert Mallet-Stevens so much he insists on having it in all the YSL Rive Gauche boutiques; Putman now refers to it as the Saint Laurent chair.

Putman met Saint Laurent years ago when he opened his first boutique in Paris on the rue de Tournon. Although she admires his clothes--"He is a young genius," she says--she wears the clothes of many other designers as well. "I feel independent," she says. "I wouldn't advise anyone to be dressed by just one person or artist. You must be yourself."

Last night's guests included U.S. Chief of Protocol Selwa Roosevelt, Marie-Helene (Bootsie) Galbraith, wife of the U.S. ambassador to France; Joan Clark, wife of the president's national security adviser; Gahl Hodges, White House social secretary; Buffy Cafritz; and Ina Ginsburg.

Those who had used the occasion to show off their new designer outfits or revive old ones sweltered in Indian summer weather. A fire last night in a Watergate basement cut off air conditioning for the complex, including the new shop. "When I saw all the fire engines, I hoped I might be heading for a fire sale," said one early arrival.