New York

There is nothing like a little controversy to stir things up. In times past, all it took was the rise or fall of a hemline. Now that skirts can be just about any length, the area of contention has shifted.

To be fitted, or not so fitted? That is the question of the moment. Should fashions for the modern woman follow the lines of the body in a way that is loose and comfortable? Or should her new clothes outline her anatomy, curve by curve, like a road map of the Alps?

The conflict arose during the first week of showings here for next spring; it was sparked by Calvin Klein, one of America's most influential designers.

Known, up to now, for the casual elegance of his easygoing yet luxurious styles, Klein did a complete about-face by presenting a collection that is as form-fitting as anything worn by Joan Crawford at the summit of her fame. Hints that such Klein standbys as roomy blousons and trenchcoats had been put on the shelf were noised about beforehand. The designer was quoted as having said he never wanted to hear the term ''sportswear'' again.

Still, who expected to see so many pencil-slim skirts that button down one side, such a lot of snug jackets shaped like inverted triangles (with the padded exaggerated shoulders favored by Hollywood designer Adrian in days gone by), not to mention the wealth of rippling peplums that accentuate tight waists as well as rounded haunches? For evening, Klein goes in for a good deal of flash, via borders of pave rhinestones and strapless colored satin bustier dresses, worn with elbow-length gloves and held up by who knows what. Such worldly clothes are not the old Calvin, and - like some of the ready-to-wear shown recently in Paris - they are confining. The new Calvin has been Europeanized, it seems.

What of the other designers whose ideas affect what America decides to wear? They are going their differing ways, but most of them are drawing attention to, and whittling down, the waistline. In some instances, the reduction amounts to what once was called handspan size.

Perry Ellis, for example, is zeroing in on the waistline with a five-inch-wide belt which is fastened with a giant buckle. It looks amusing but is probably no easier to wear than was the Iron Maiden. His corselette belt is one of many satiric touches in a charming collection that is concentrated chiefly on cotton handknits and linens. The wide belt goes over long skirts with fullness gained through unpressed pleats, and short linen coat dresses given double-breasted treatments with rows of oversized mother-of-pearl buttons.

The cinch belt is actually the only constricting item in a generally lighthearted collection. Peg-topped skirts and culottes have extra-deep pockets and come in summery striped cottons. The most playful Ellis creations are the trompe l'oeilm sweaters. Once off on the tricks of fooling-the-eye, there was no stopping Ellis. He has knitted in bowknots, boutonnieres, lacelike collars, and large emerald-cut jewels. For the men, he has white pullovers with intarsia neckties.

As for Ralph Lauren, whose styles seem eventually to reach all and sundry, he is leaving the waistline alone and not otherwise advocating closely fitted fashions. He strives for perfection and often achieves it in such pure and simple linens as a tailored two-button coat dress or a beautifully cut shift in unadorned black or white. Pastel handkerchief linen tops and pants accented with fine bits of embroidery carry out his penchant for combining the best of the old with the best of the new. Big pieces of abstract lucite jewelry are all over the spring fashion scene, but Lauren adds only a superb rope of pearls or a small antique marcasite pin. The black patent sling-back pump with a classic high heel is another choice accessory.

Stripes, the outstanding graphic in last spring's fashion picture, are given their due by Adri. Instead of the strong contrast of black and white, her combinations tend to be tone-on-tone pale mauve or gray with navy the leading dark in her stripe-on-stripe fabrics. Linen, chambray, and seersucker are the prime materials she uses with the easy-to-wear knit tops she calls ''bodywrappers.'' These are now being produced for men as well as women.

There is no perceptible tightening up of the silhouette at Anne Klein, where designers Donna Karan and Louis dell'Olio restrict the colors to ivory, black, and cinnamon. Thus their separates of silk tweed, jacquard, cashmere, and gossamer-thin gabardine work well together in any number of combinations.

A little less yardage and the occasional optional wide belt are the only concessions to closer fit that are evident at Albert Nipon, where daughter-in-law Lois Nipon reports, ''Our dresses have slimmed down a little.'' The tailored coat dress, a style to watch for next season, is handsomely executed by the Nipons in a single-breasted version with hemstitched details and comes in either black or white linen.

For Pauline Trigere, whose couture-class clothes are made to last, the matter of fit is an inbred skill. The shoulders of her tailored-to-the-nines three-piece suits of double-face wool are more pronounced for next season, and the link-button closing on the jacket is a new note. Chemise styles that skim the body predominate at Trigere, but she adds a wide belt to some dresses. Mixtures of dots with stripes in silk dresses with companionate coats are among the daytime choices. The clothes are becoming and timeless - and not at all controversial.