Sportswear out on the town

Active sportswear is changing the fashion scene. No longer the unpolished country cousin, seen only on tennis courts and golf courses, sportswear now goes out on the town.

Warm-up suits and sweatshirts have shed their drab gray, fleece-backed fabrics and are into lush velours. Golf clothes and jogging suits, and various other items are now edging their way into places where a crisp cotton or linen dress used to be de rigueur.

The trend is not totally new, but is rapidly gathering momentum. Tee shirts stretch out to dress length and go out to dinner. Cashmere is appearing in sweat-pant styling. Knickers are seen more on the street than on the golf course where they started. These items crop up in places like movies, luncheons, and shopping malls.

''Women today want clothes that are attractive enough to eliminate the necessity of running home from the tennis court or country club to change into a dress merely to pick up the laundry or have a quick lunch with friends,'' says one experienced fashion observer. ''It's at least a saving on gasoline, not to mention time and personal energy.''

Fashion designers and buyers say there are many reasons for this demand for go-everywhere sportswear. The classic, timeless styling all but eliminates obsolescence, they say. The rules of the games and club dress codes don't change very often. Further, this styling does away with any controversy over hemlines, silhouettes, etc.

Sport dressing takes away a lot of the risk and uncertainty many women feel about coordinating their colors, say some, because the whole scene (with the exception of tennis dresses) is one of coordinated separates.

Also, this type of attire demands little in the way of accessorizing. In fact , a change of shoes changes the mood of the outfit.

Sonja Caproni, fashion director for all I. Magnin stores refers to this look as ''Saturday Clothes--clothes for the participants or those who just want to look the part.''