Just as the inaugural fashion spree cooled down in Washington, the big-league stuff started down the runway in Paris.

This is the week top French and Italian fashion designers show their wares for the spring season -- with price tags that never dip below $1,000.

The big show stopper this season was the appearance of Brooke Shields on the runway at the Valentino show in Rome. Last year Shields was spotted watching the Yves Saint Laurent show, an apparently the photos of her printed in Harpers Bazaar were so attention-getting that Valentino decided to go YSL one better and have Shields modelhis clothes live. The audience loved seeing her in silk bloomers worn with a see-through lace top.

It was the YSL show yesterday that is expected to have the most prolonged impact on fashion, partly because the clothes will swiftly be translated into his ready-to-wear styles for his Rive Gauche boutiques in Washington and elsewhere. The SL collection, which he called Homage to America and showed to the music of George Gershwin, revived a favorite YSL silhouette -- putting emphasis on the dropped waistline. He did this using the battle jacket and droppedwaistline dresses of chemise shaped tunics over pleated skirts, as well as by accenting the derriere with a low-placed bow. "Not meant for sitting down," commented one observer. Saint Laurent also showed several mannish pin-stripe suits, softened with print over-blouses and ties or ruffles.

Emanuel Ungaro's collection played with every available luxury fabric, sometimes combining serveral of them -- such as lace, brocade and printed silk all in one costume. He likes the slightly fitted princess silhouette, often ending with a ruffle at the knee. And like YSL, waistlines are often dropped below their normal place.

The Chanel salon is still boarded in front from the recent bombing but the show, and the clothes, looked most traditional in the usual second floor setting. Apparently Nancy Reagan is not the only first lady who appreciates Chanel's classic styling. In the front row of the Chanel show was Claude Pompidou, whose late husband was president of France.

To cope with crowds, the Dior show was moved from the salon to the Hotel Crillon. The spring line includes paintsuits with wide,-ankle-length trousers, as well as the drawstring theme on easy dresses and even on an evening coat.

Givency showed some of the shortest hems of the season, with several of his suits and many of the printed chemise or tunic-over-pleated-skirt styles cutting off above the knee.