NEW YORK, OCT. 31 -- Where has the sleeveless dress, short and smart, been hiding all these years? In a maze of pants? Judging by the American spring collections so far, one would have thought it was a recent discovery. And in a way it is.

Seventh Avenue's Ode to the Dress added another verse today when Ralph Lauren's willowy models hit the runway in thigh-skimming shifts. Some swirled in diagonal bands of red, white and blue, which sound patriotic but aren't. A khaki rayon jersey number swooped over the hips. A few were cinched with wide woven belts, notably a sage suede shift. The only adornment for a blond leather shift was a chocolate scarf tied at the neck.

This time Lauren steered clear of rodeo, fishing and golf scenes. Nor is the timing right, apparently, for another of his recent excursions, military wear. If he's reading the tea leaves correctly, women now want sportive simplicity and colors as soothing as a nursery pudding: banana, vanilla, robin's egg blue.

Just about everything resorts to the body for shape -- lean rugby-striped jackets, bare-back jersey dresses, abbreviated tops thinly striped with black and brown wooden beads. The clothes are young but not innocent.

By noon the flotilla of black hired cars carrying retailers, socialites and editors was moving slowly across town to the Plaza Hotel, where Oscar de la Renta was about to praise the dress. But then, if anyone understands this new best friend, it's de la Renta.

For nearly every chemise and scoop-neck dress there is a jacket, a twice-told story for day and evening. His double-faced wool jackets sometimes have flat shirt collars or none at all. An awning-striped coat in cedar green, ice blue and mustard shrugs off an ice-blue V-neck dress. Over a pistachio linen dress he buttons a long and slender acid-green wool jacket.

There's something of the New Frontier in these clothes, especially one sleeveless gown in pumpkin Shantung with a puffy skirt and a neat bow at the waist. It could have appeared in a Washington ballroom circa 1964. On the other hand, one senses a kind of Spartan simplicity in an A-line melon Shantung coat over a high-neck chemise. Oddly, it's also a theme pursued by Sybilla, the Spanish designer, but in more proletarian clothes. Both look right.

Perhaps as a concession to these less than giddy times, de la Renta's evening embroideries are low-key. There are a few brocade coats and some lovely white pique jackets embroidered with pink rosebuds, but ultimately the story is the dress.

All week long designers have been promoting the "7th on Sale" benefit for the New York City AIDS Fund to be held Nov. 30 through Dec. 2. The public sale of designer samples and overruns is the first collective effort by the industry on behalf of AIDS victims. Many designers have taken their final bows wearing or waving "7th on Sale" T-shirts.

But designers are also unified, more than usual, on sartorial themes. Carolyne Roehm's dressed up collection reintroduced cotton pique in boxy fisherman tops and the season's popular trapeze tunic in Mediterranean stripes. Daisy eyelet coats run toward a mod posey message, but her baby-doll dresses with preposterously large skirts and tiny bodices simply ran aground.

The best show in town occurred Tuesday morning in Calvin Klein's beige showroom -- not on the runway but on the sidelines. Socialite Nan Kempner was seated next to record producer David Geffen, who was next to writer Fran Lebowitz, who was next to pregnant "Today" anchor Deborah Norville, and so on. Bianca Jagger wore sunglasses and a fur hat. People blew kisses across the runway at friends they hadn't seen in at least a day, while a dozen or so photographers rushed to take their pictures.

If only Klein's clothes were as interesting as his guests. The designer takes minimalism to such an extreme that one has the feeling his skimpy silk T-shirt dresses and wispy georgette wrap blouses might evaporate at any second. Even those subdued noncolors -- adobe, parchment, clay and almond -- look as though they might crumble and blow away.

Klein clearly wants to remove the distracting details -- prints, pockets, buttons, make-up and stockings -- and concentrate on fabric and cut. His long collarless jackets skim over collarless blouses left untucked over fluid silk shorts. A pale citron suede parka looks like a favorite sweat shirt, all soft and droopy. Slender crepe pants perform like leggings, and many of the washed silk dresses and skirts are cut on the bias, a technique that gives clothes more contour.

But such subtleties beg the question: When will Klein move on to something that isn't beige, High WASP in riding boots or stock-in-trade minimalism? Pared down clothes almost always look pleasing, but the trouble is that there's little room left for innovation. His clingy evening minis that were once done in lace, then sequins, are now covered in a caviar spread of wood beads or tiny pearls. But the dress is still the same. Only his finely ribbed knits -- a navy rayon unitard, a bright mango cashmere jacket -- offered a contrasting note to the tune played at the beginning of his show, the Pet Shop Boys singing "Being Boring."

Jennifer George staged a teeny-tiny show in her Seventh Avenue showroom. Her clothes are relaxed with a whiff of dressed-up luxury, and she handles the trends in her own way. Inspired by "the glamour of post-war Society," George does the inevitable poplin shift dress, the classic white pique raincoat and the season's big retro favorite, the big shirt.

But she isn't entirely seduced by the Babe Paley era. A white damask pique jacket -- simple but rigorously cut over the hips -- is lean and modern. Her smudged-disc prints in pink, orange and chartreuse on ivory crepe are pop-op without a '60s refrain.

Christian Francis Roth put on his graphic show late Tuesday evening in the jammed auditorium at the Fashion Institute of Technology. A lot of FIT students sneaked in to watch Seventh Avenue's bright young thing turn currency into fashion, or visa versa. His organdy dollar bill print dresses and tunics are fun, as are black suits printed with large dirty pennies.

Critics have wondered if Roth, known for his surrealist appliques of bottle caps and sharks, can rise above kitsch. He can. This season's cubist Matisse and Picasso separates -- intricately composed of dozens of pieces of inset fabric -- are wildly imaginative. But his milkmaids in satin tulip petal skirts should be left on the farm.

Tonight, the spotlight shifts to Giorgio Armani, who's hosting a dinner for 250 at the Museum of Modern Art, where the ode de la mode will no doubt be Spartan chic in beige.