Autumn lines: long, lean, low-key

If fashion is a reliable indicator of the mood to come, we are in for a low-key fall. Subdued styles of the classic genre were the clothes that stood out in the showings for next autumn and winter held here recently.

There were sprinklings of glitter and flashes of vivid color at some design houses; but the major message is one of sporty, laid-back elegance, so understated they at times verged on the severe. Clothes that make their fashion points quietly - via long, easy, clean lines and discreet tones - had the most impressive impact. Many new fashions are based on men's clothes. We are to look like ladies while dressing somewhat like gentlemen is the general idea.

The feeling was nowhere so apparent as at Ralph Lauren, who presented his collection of menswear flannels, somber tweeds, cashmeres, and dark velvets in the library of that bastion of conservatism, the Union League Club. Nothing beats the perfection of a beautifully tailored white silk blouse with a slim chalk-stripe wool skirt or pants - or so the designer seemed to be telling us with the opening pieces at his show.

The convent-like look of a white round-collared shirt under a cashmere sweater dress or a flannel jumpsuit carried the prim-and-proper theme along. The white silk shirt also appeared under narrow navy flannel suits that seem ideal for women who have achieved board-room status.

In keeping with the book-lined paneling of the league's library, colors were rich but muted. Tattersall-patterned cardigans, Fair Isle sweaters, and cabled twin sets are as apt this time to be paired with velvet skirts or pants as with wools, which makes a change.

Lauren's big polo coats are sleeker than most oversized topcoats in a season when huge, all-enveloping coats are everywhere. There's a black velvet trench for late day. Antique marcasite pins and lace collars are Lauren's only concessions to ornamentation.

Of equal note: the spare simplicity at Calvin Klein. Everything on his runway was, however, on a much larger scale. His button-front shirt dresses (they come in wool jersey and silk plaid) have sweeping skirts that almost reach the ankle.

Coats, whether raglan, balmacaancq, or military trench, are imposing in size. Here again, the white silk shirt runs through the collection, proving that you can't have an oversupply of that item in your future wardrobe.

Over the cuffed trousers and the riding skirts (they come in assorted flannels, gabardines, and cavalry twills) goes a wide-shouldered straight-cut blazer so roomy it might have been borrowed from your brother or your husband. Black opaque stockings with men's patent dinner pumps are the regulation footwear.

There isn't any razzle-dazzle for evening: just covered-up white georgette blouses with bouffant skirts, moire suits with cashmere sweaters, and a series of unadorned black velvet gowns with long sleeves but low-cut backs.

Jumpers, which haven't been around for a while, were back in force at Perry Ellis, who showed elongated hip-banded styles over geometric print blouses. (His one-button jackets are lengthy, too.) Ellis dedicated his collection to Sonia Delaunay, the French abstract artist of the 1920s, whose brilliant designs he has translated with spirit onto sweaters, shirts, the borders of knit tunic dresses, and even a voluminous fur coat. Cloche hats that hid the models' faces, suede pumps with little curved heels, and fur capelet stoles were part of the picture.

It promises to be another big sweater year: That article of apparel made its slouchy way from day into evening at the showings. It took the form of double-breasted jackets, coats, and dresses, besides the everpresent twin sets. Adrienne Vittadini's fancifully stitched dresses and tartan patchwork knits looked especially appealing. So did Sal Cesarani's navy shetland dress with a bright-colored Fair Isle yoke.

Underplayed, oversized dressing isn't for everybody, and some designers recognize this. Both Oscar de la Renta and Bill Blass dropped their knee-length hemlines appreciably but kept the proportions of their city suits within moderate bounds. Clear, bright colors in their collections - stinging pinks and greens at de la Renta - balanced out the prevailing darks and neutrals. Beading (which covered sumptuous sweaters at Blass), lavish fur trims, and yards of stiff satin will keep lovers of luxurious looks happy.

If that doesn't suffice, there are Halston's sequin-paved dresses with waterfalls of fringed beading spilling off the shoulders, and his capacious velvet ponchos bordered with fox. Glamour lives.