The stylish coat dress

One of the fashions to watch for spring (next fall, too, for that matter) is the coat dress. Sort of a hybrid style, it combines the best features of a lightweight tailored coat with a semifitted dress.

Its prospects for universal acceptance are looking good. For women who are thinking of expanding their working wardrobes of separates by acquiring a dress, this dependable style has a neat, upscale appearance that makes the right impression at the conference table. When dressed up with appropriate accessories , a coat dress is sleekly attractive at a candlelit dinner in a restaurant, too.

It suits almost any age, and its simple cut flatters most figures, from size 4 to 18. Its assets are, in other words, manifold, and there is no reason why the coat dress should not become as much of a mainstay as the chemise, which has been a proven success over a long spell.

You could not call the coat dress a sleeper, exactly. It has been making its points for some time in the higher reaches of fashion. Noticed for its clean straight lines in the collections of such key designers as Saint Laurent and Ralph Lauren, the elongated dress with attenuated lapels and side-wrapped skirt has made news as ''the boardroom dress.''

Some coat dresses have low necklines framed by long narrow lapels. Other versions of the style have broad collars - like the contrasting black one on Calvin Klein's belted dress. Evan-Picone is bringing out a Chesterfield style with a velvet collar for fall.

For something so basic in design, the coat dress is a theme that seems to have plenty of variations. There are sharp contrasts of black and white in collar and cuff treatments, and the style exists in single- and double-breasted as well as side-wrapped, one-button forms. Buttons tend to be larger than life this season - like the oversized mother-of-pearl buttons Perry Ellis puts on his wide-collared coat dresses.

Some coat dresses take well to the addition of a big belt. Others, the kind that are cut to narrow down from a broad shoulder line to a slim hipline, are best worn unadorned.