Forget the Fads : Fashion: Big and not-big-yet New York designers seem to suggest the same thing in their fall lines: ‘Find your own style.’

NEW YORK —  As designers continue to show their fall ’91 ready-to-wear collections here this week, most of them seem to be struggling with the same question: How to approach fashion when more basic concerns demand attention.

So far, the clearest, most convincing answers have come from two of the best-known and two of the least-known names: Ralph Lauren and Calvin Klein, and Todd Oldham and Christian Francis Roth.

Their collections look nothing alike. But the philosophy behind them seems to be the same: forget about trends, find your own personal style.

Lauren, an established protector of the American spirit, keeps the flame alive with his fall line, and the timing couldn’t be more appropriate. A red, white and blue assortment of activewear had snappy brass buttons and military gold braid. A skier’s white jumpsuit with epaulets looked especially new and adaptable to streetwear. So did a pair of white wool ski pants tucked into black flat-heel ankle boots. He showed them with a standard-issue-style Navy crew-neck sweater and a black leather belt bag at the waist.

Among his blond- and camel-colored outfits for day, a short coat with a circle skirt, belted in suede, was a standout. Tartan plaid--a theme in most fall collections shown this week--was mixed with velvet for a clean, energetic brand of elegance. There were plaid coat dresses with military brass buttons, body-contoured plaid peplum jackets over narrow pants, and mid-thigh-length tartan shorts that flared slightly away at the hem, worn with black velvet turtlenecks.

The best Lauren evening wear was a Wedgwood-blue satin jacket with a portrait collar, sashed over narrow-cut black silk pants.

At the end of the show, Lauren walked the runway in faded blue jeans and a used (designers would say “recycled”) shirt inscribed: “Wabash Valley Motorcycle Club, Terra Haute, Indiana.” Does this mean he is doing his part for a cleaner environment?

Calvin Klein stayed true to his well-established, Italian-inspired style; he even opened his show with the monastic-sounding choir music that Romeo Gigli has made fashionable.

Klein’s collarless coats in sage green or silver recalled the clerical robes that both Gigli and Giorgio Armani have adapted in recent collections. And his subtle, paisley shirts, with rich-looking silk mufflers to match, were shaped like the long, pared-down shirts for which Armani is known.

But as always, Klein made these elements his own, mixing them with velvet stretch pants, tweed jackets, skirts with subtle slits and funnel-neck tunics in richer than usual color combinations such as gold, plum and chocolate-brown.

The newest update in Klein’s controlled and gradual evolution from American archetype to Italian icon was a jacket dress with small collar and high buttoned closing. He showed it in heather tweed over rib-knit tights. Cut shorter, the jacket dress went over narrow skirts or velvet stretch pants.

Klein’s steamy, lingerie-like evening dresses in gold or silver lace were molded to the body.

Oldham, a transplanted Texan, and Roth, a native New Yorker, have been building their fashion vocabulary for a far shorter period of time than Klein and Lauren. Oldham opened for business last year, Roth about two years ago.

Each works on a small scale, often by hand. Each mixes artistry, wit and technical skill, and dips into American culture for inspiration.

But Oldham is rowdy while Roth is cerebral, and, this season at least, Oldham is urban while Roth is rural.

Dallas-born Oldham’s around-the-world collection was a kooky trip with beaded Persian carpet skirts, Bengal tiger-print pants and woven potholder pockets on suit jackets.

One bowling-league-style jacket looked as if it had been inspired by Watts Towers; it was covered with buttons and beads. A “been there” pantsuit was covered with sequined postcard images from Idaho and Japan.

It was all very glamorous, playful and smart. And it all started with a weekend trip Oldham took to the Smithsonian Institution in Washington. “In one day at that museum I saw things from almost every culture in the world,” he explained after his show.

Roth’s fall collection began when he made a study of Amish quilts, then re-created them as skirts with matching shawls, strapless dresses with full-size quilts for wraps and “hobo” pantsuits with quilt-patch details.

A floor-length circle skirt, and a wedding dress with wedding ring appliques on the skirt and train were far more than items to wear. They were garments to keep, display and pass on through generations, just like the quilts that inspired them.

“These clothes are about women saying, ‘I don’t want to look like I’ve been cut from a cookie cutter,’ ” Neiman Marcus Fashion Director Joan Kaner said.

“People want to be more creative about the way they dress. They are mixing flea-market finds with designer labels.”

Rodeo Drive boutique owner Fred Hayman had his own explantion for the appeal of Roth and Oldham.

“I carry the lines because they are hot,” he said. “In many ways, hotter than the young Europeans. Roth and Oldham make items; they make pieces, not ensembles. And that is what younger-thinking women want. People don’t shop the way they used to. They don’t buy as much.”

Other designers’ collections that made sense kept things simple and uncontrived.

Michael Kors showed basic shapes in luxury fabrics--but not before a near disaster almost wiped out a considerable portion of the fashion press. In the downtown loft where he presents his line, part of the plaster ceiling gave way and shattered on the floor, centimeters away from New York Times Magazine fashion editor Carrie Donovan, Suzy Menkes of the International Herald Tribune and several of the best fashion stylists in the city, as well as Bloomingdale’s Senior Vice President Kal Ruttenstein.

After that, Kors turned down the music but went on with the show. He mixed cable-knit tunic sweaters with sequined stretch pants, and layered leather dirndl skirts over camel-colored knit sheaths. Powder-pink or pale yellow leather anoraks (short coats) gave a look of luxury to the simplest dresses or tunics or skirts underneath.

A black and white striped satin dress with a short skirt was one of the better full-skirted coat dresses seen this week. And every designer has one.

This was not one of Kors’ best collections, but he was true to his formula: night and daytime fabrics mixed together, and lean clean sportswear shapes.

Adrienne Vittadini used bright colors to enliven her fall line. A quilted satin evening coat and a short, sequined T-shirt dress were combined for a collision of red, orange, fuchsia and gold. She bumped fuchsia suits against orange sweaters and tights. A synthetic sable coat, worn over a cable knit dress and pale suede boots, made for a quieter and classier ensemble.

Carolyne Roehm dared to bring back real fur--seldom seen in designer collections these days. Her claret-dyed mink coat slipped over a body-molding navy-blue dress for one of her best daytime outfits. For evening, heavy silk cocktail coat dresses with short, full skirts were pinned at the waist with diamond brooches.

Oscar de la Renta, Roehm’s mentor and friend who was seated in the audience, must have appreciated her luminous silk caftans, which he often includes in his own collections. Geoffrey Beene might have liked her navy-blue gowns sliced with chiffon insets in the bodice, had he been at the show. But Roehm hasn’t been alone in letting outside influences show this season.

Along with her bow to De la Renta and Beene, as well as Klein’s bow to Armani, Bill Blass gave Beene the nod when he mixed patterns in his lace cocktail dresses worn over lace hosiery.

It’s been that kind of season.