Spring fashions; Hemlines are long and short, sportswear dominates, and dresses are gaining in popularity

CLOTHES for spring are pared to the essentials: clean lines, quality materials, no fussy details. Minimalism, a much-used word these days, has found its place in fashion.

Yet within this simplified framework there exists plenty of room for differences in approach so that those who do not see themselves in unadorned natural linen (the season's premier choice) will not feel disadvantaged.

Some of the differences almost amount to altercation. The hemline gap, for instance, is wide enough to seem unbridgeable. Certain key designers whose moves are closely followed by younger women favor skirts that edge toward the ankle. Ralph Lauren, Norma Kamali, the Anne Klein team of Donna Karan and Louis del'Olio, and Calvin Klein are in this long-skirt brigade, joined by many of their European cohorts. (Perry Ellis is hedging the question by showing both short and long for daytime.)

It's curious that after having stressed the unimportance of hem lengths for several years, designers are now expressing strong opinions about them. But there you are. That's fashion for you.

The outcome of the short vs. long controversy of course depends on what women themselves decide to wear. Some will go along, according to whim, with the ''variety of lengths'' idea. Some will stay with the particular hemline that suits their personal taste and mode of life. Others can sidestep the issue by wearing pants, which again have a high fashion standing - except for the office.

There is much diversity in styles of dress. Sportswear still dominates, although the dress is a big contender against separates.

Tailoring has lost the sharp edges. A prime example: the linen duster - a long, relaxed, unlined trench done especially well by Ellis and Lauren. Like the full-backed shell coats in lightweight wool, silk, or cotton shown by Geoffrey Beene and others, this type of coat floats like a breeze. It's the newest day (into evening) cover for dresses and pants, and likely to take over the role of the jacket.

Sportswear proportions are looser, shapes have breadth across the top, and lines are longer. The stretched-out cardigan, introduced last fall, carries on. As a suit jacket, it is often belted.

Whether it's a knee-length chemise dress, a pair of straight-cut trousers, or a kimono-style topper over a mini, the effect is elongated and uncomplicated. As to details: tucks and pleats, yes; frills and ruffles, no. Fancy trimmings are nonexistent except for sequined beading on some of the more expensive evening regalia.

Basic colors are natural (going from cream to putty beige to sand, terra cotta) and black. There's much use of tone-on-tone mixtures of texture - crepe de Chine or poplin with linen, for example.

Shocks of vivid color - such as a sharp yellow jacket over a black dress, or a turquoise belt with an all-beige outfit - are the effective pickups. One snappy accessory in a bright color often does the trick.

Many new fashions have overtones of other times and places. Ralph Lauren's Victorian theme for spring brings to mind what the wives of English planters might have worn earlier in this century in Ken-ya. Perry Ellis drew ideas from the Australian outback (as it might have been) and from the yachting scene down under.

The nautical/regatta influence is present elsewhere in a lot of crisp navy and white fashions this season. A case in point: Albert Nipon's Deauville suit, composed of a slim jacket with a striped asymmetric lapel and a pleated skirt.

But modern-day influences are not absent. The overall is gaining on the jump suit as a hot fashion for the young and frisky. It comes in all sorts of fabrics - flowered seersucker, abstract-print poplin.

Then there's the cotton knit tank layered over a T-shirt, with one shoulder bared a la ''Flashdance.''

A popular look last summer, it's risen from the ranks to high-fashion rating, having been picked up by Karl Lagerfeld and Calvin Klein, who gave it new interpretations. Klein's is a U-neck black cotton knit mini over a handkerchief linen T-top.

Style doesn't always filter down, as Conde Nast once said. It often filters up.