FALL FASHION

"Opulence" has been the word of the hour here lately as US designers rolled out the red carpet for new fall-winter fashions. There is no escaping the 1981- 82 mode for affluence: It extends throughout the spectrum of dress from dawn 'til dark.

Styles, colorings, and sources of inspiration are eclectic and upbeat. While the clothes have much flair, they are soft and relaxed and should be enjoyable to wear.

Luxem -- or at least a touch of it -- is the overall rule, applied to fashions for the careerist and active homemaker as well as the woman who leads a purely sybaritic existence. Fall's tailored basic is more likely to be a velvet spencer or mohair greatcoat than a flannel blazer or gabardine trench.

Besides largessm in yardage (the Americans more than equal their European confreres in wide, full layerings of fine materials), there are expensive leather and suede garments in nearly every major collection. Lavish metallics -- pipings or whole garments of smoky bronze, copper, or pewter leather (as well as lurex-threaded wools and glistening gold lames, laces, and brocades) -- may be foreseen as the lights of fashionable women's lives. At Bill Blass and Oscar de la Renta particularly, fur trims and liberal doses of beading, embroidery, and other costly details have been extravagantly applied to ultratich fabrics.

The anticipation is that price standards will measure up to the luxuriousness of the fashions themselves. Nevertheless, the "Will it sell?" question does not greatly perturb the industry.

Fashion observers note that although customers have been buying less lately, they are definitely buying better clothes. While sales figures for lower- and moderate-priced fashions have not been heartening, top-drawer merchandise has been walking out of the stores.

Thus the pattern of the American woman's buying habits is seen to be changing , coming closer to the European's preference for quality over quantity. "No woman wants to throw things out of her wardrobe because they look so totally dated. Nobody can afford that any more," says Rosemary McGeary, vice-president and fashion director at John Wanamaker. "Now a woman is going to buy that one fabulous suit, skirt, jacket, or one soft blouse and add it to her clothes from other times. Or she'll invest in one truly good accessory -- the good shoe, belt, handbag, or the shawl that all of a sudden updates the good suit she paid a lot of money for last year."

Thus there is hope for the person with the slim fashion budget. Among the smaller acquisitions Miss McGeary cites as ideal and relatively low-cost ways to bring what one already owns up to fall's fashion mark are "colored hosiery" and "the new wonderful metallic accessories" -- both of which made repeated appearances on the runways at the recent showings.

While some Americans -- notably Geoffrey Beene, Perry Ellis, and Adri -- show an independence of spirit that would be beneficial to their less venturesome peers in Europe, other US designers follow going trends from Paris, Milan, and London.

Interpretations of the Cossack coat and swirling tent shapes over long circular skirts almost invariably wrapped at the midrifF (the point of control), with extremely wide belts, are continuations of main themes shown overseas earlier this spring. So were the lower heels and cuffed ankle boots in the US collections.

The alternative look is the narrow tunic over a short skirt. Short cardigans or fitted jackets over full skirts, smock styles, and the bubble chemise are some of the other leading shapes.

Diversity, it is plain to see, is more rampant than ever. Nearly every style has its opposite number. For each ankle-grazing flared skirt at Perry Ellis, there's a pert, above-the- knee straight skirt; for every pair of gathered bloomers, some closely knitted knee pants.

Trying to pick the sleeve of the season would be a waste of effort. Capacious sleeves, which are replacing padding as shoulder emphasis, may be kimono, cavalier, raglan, bell, Byronic, batwing, or leg-of-mutton, so long as they give a certain width. Ellis does it by adding a pinafore frill to the shoulders of puffsleeve coats and sweaters.

Options in role-playing have also increased. At Ralph Lauren, elegant Fred Astaire-type sportswear and clingy satin bias-cut Carole Lombard evening dresses are counterpoints for a group of Santa Fe blanket wools, suedes, and stunning handknits based on authentic Navajo patterns.

Even without the collector's-item silver and turquoise conch belts Lauren showed with his Southwest American Indian clothes, fashions like his ruffled prairie dress of pale yellow chamois leather demand a hefty bankroll. His chamois dress, for example, will retail for around $1,350 -- which does not take into account the upkeep, bound to be considerable, as chamois needs frequent cleaning.

Elsewhere, Anna Kareninas came down the runways (in droves at Oscar de la Renta) and Moroccan dancers mingled with Marilyn Monroe looks. Regency dandy, Elizabethan effects (including a Mary Queen of Scots evening outfit at Bill Blass) and Scottish mixtures of heathery tweeds with outsize muted tartans and dark paisleys were part of the picturesque panorama.

Volume -- the big message -- is expressed through multiple layerings of ample yardage. The change is most marked at Calvin Klein, who has gone from minimalist dressing to generously full, with, for example, his new leather-piped blanket plaid coats. Capes, ponchos, hooded duffels, capelets, shawls (rechristened "sweeps" in fashion jargon), and oversize mufflers are the main toppings in the layering game.

If this rings a familiar chord, it should, for it is essentially a replay of the "big look" of four years ago. Working in the vein of what Adri calls "a continuum of fashion," many designers have revised their own successful classics.