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AUTE couture belongs to Europe, but sportswear ``is an American invention, an American industry, and an American expression of style.'' So says Richard Martin, executive director of the Fashion Institute of Technology (FIT) here in New York, in introducing an important exhibition that salutes our native gift for creating attractive, practical, easygoing clothes.

One look at ``All American: A Sportswear Tradition'' (on view until the end of June at FIT's Shirley Goodman Resource Center) brings a nod of agreement with Mr. Martin's appraisal. It is clear that as long ago as the last century, today's concept of clean separates dressing was on its way -- prefigured by the linen shirtwaist tops and pleated skirts worn by golfers in the 1890s, for instance. As for workout clothes, our early gymnasts were on to the mix-and-match idea well ahead of the rest of the world, exercising in various loose blouses and Zouave-style trousers that were probably inspired by the campaign Amelia Jenks Bloomer had waged for dress reform.

While it makes its points through such historic examples, this new exhibition is not primarily a retrospective. It is instead what associate curator Harold Koda describes as ``a combination of modern with vintage sportswear,'' featuring side-by-side displays to illustrate near-relationships: that of a '20s tennis dress with, say, a Calvin Klein or Ralph Lauren simple crepe de Chine. Sometimes these relaxed-looking contemporary clothes are difficult to distinguish from the forerunner fashions. A two-year-old Perry Ellis two-piece striped knit is among the exhibits with the kind of uncluttered, ageless quality that withstands the test of time.

``The importance of function in active sportswear minimalized the use of decorative detail and did away with the complex inner construction you find in couture,'' says Mr. Koda, who worked closely with FIT curator Laura Sinderbrand, producer of the exhibition. ``Most of the early pieces in the show were mass-manufactured. Ease of care was another major concession when the notion of sports separates began.'' The shapes are of the period, but such field-and-stream attire as the leg-of-mutton-sleeve jacket worn by fashionable fisherwomen, circa 1905, was not too constricting, and it could be laundered.

Americans, both men and women, want comfort, and the high value they put on it has been a strong factor in active sports design. In the 1920s, patternmakers at the Arrow Company came up with a ``Negligee'' shirt that Wimbledon champion ``Big Bill'' Tilden wore. It had deep armholes and a shawl collar very unlike the stiff ones on the dress shirts seen on the Arrow Man in the famous advertisements. (The company has lent many of the paintings that J. C. Leyendecker did for its ads and has provided financial support for the FIT exhibition.)

The word from Paris meant everything in fashion up until World War II, when France was cut off and American designers had their main chance. Most of the greats of those pioneering days -- Claire McCardell, Bonnie Cashin, Vera Maxwell, and Tina Leser, among them -- are well represented here. McCardell's many innovations include Jasco jersey tights (similar to the dancers' leotards she put into fashion currency), the pullover with a funnel neck that converts to a hood, and the denim ``Popover'' dress. Her romper bathing suit in black and white cotton plaid is starred in the beachwear display, along with Rudi Gernreich's notorious topless suit (shown from the back) of the 1960s. Bonnie Cashin's practical eye brought in the layered concept, canvas rainwear, hardware closings, and other experiments that have become part of the sportswear vocabulary.

Perhaps the most telling sign of American sportswear's reach is the 1984 evening turnout by Bill Blass: a tunic-length cashmere sweater in salmon pink matched with a bouffant slipper satin skirt. It is possibly the all-time high in casual chic.