If your sport is slithering down the slopes at rocket speeds, there are plenty of wonderfully colorful and ultra-practical ski togs in specialized shops and department stores this season. Skiing may have emerged as the No. 1 sport in Japan, but curiously enough it is China, where the average person probably thinks a ski pole is some kind of exotic Occidental fishing rod, that is the current influence on winter sportswear.
Jackets and vests made of feather-light fabrics, quilted and interlined with eiderdown, trace their origins back to Chinese coolies, who discovered the attributes of layering several centuries ago. They would probably be startled to find themselves immortalized as fashion stars in the current European firmament.
In the past glory of Imperial China, only the wealthy mandarins could afford to wear silk. Peasants dressed themselves in baggy cotton trousers and layers of cheap cotton smocks until they gradually realized that one jacket could do the work of three or four if it was padded with eiderdown. The trend has somehow managed to make it from Manchuria to the Champs Elysees, where it has been christened ''doudoune'' in French.
All these jackets and skiwear appear in chintz, cotton, satin, poplin, and nylon. These cloud-weight fabrics are interlined with real eiderdown, like a German quilt, or fluffy synthetics that prove to be equally warm and lightweight , though the visual effect tends to turn even a wand-slim skier into a replica of Humpty Dumpty.
Many parkas, blousons, and anoraks are completely reversible, switching from flannel or tweed to sheer waterproofed fabrics. Another gimmick features removable sleeves that zip out beneath the shoulder epaulets. It's a great idea for late spring skiing or just loafing about on some sheltered terrace high in the mountain sun. But since most of these jackets are quite expensive, one might as well get full value by wearing the sleeves.
With 50 million skiers in the world and two-thirds of them in Europe, it's not surprising that two major salons in France alone are devoted to skiwear. The ''Snow and Mountain'' exposition is held every fall in Paris, and the International Salon is staged at Grenoble early in March.
Lothars and Jantzen, two famous names once exclusively associated with bathing suits and summer sportswear, have recently branched into the lucrative field of winter sportswear.
Lothars, a German maker that opened in Saint Tropez in 1969 and put the ''Blue Men'' of the Sahara on the fashion map with faded tie-dye cottons, has made an easy transition from sun to snow. It has replaced cotton with synthetic fibers for long outer coats and jackets quilted over thistledown inner linings. These garments are almost hermetically sealed, yet are amazingly warm and lightweight. Jantzen, synonymous with bathing suits practically as long as anyone can remember, is also on the quilting bee, turning those sleek young mermaids of summer into bulky but very unabominable snow maidens.
Like ''La Nouvelle Cuisine,'' the revolution in French cooking during the past few years, there is now ''Le Nouveau Ski,'' with all sorts of nouveau togs and terms to cope with it. While the majority of skiers stick to classic downhill (known as ''Le Straight Down'') or cross-country, where gear is usually based on the fact that one is less likely to tumble in the snow, new fads are taking over. Many of them appear to have come from the United States: the mono ski, the ski bird and ski surf, and acrobatic skiing, which is known here as ''Le Hot Dog.''