It is a good designer who knows his customers, and Oscar de la Renta didn't have to go far to find his yesterday. The faithful were out strong -- at least 30 strong -- for his fall fashion show at the Parsons School of Design. They are the trim and the attractive -- such as Nancy Kissinger, Pat Buckley, Ann Getty, Mica Ertegun, Evangeline Bruce and Annette Reed (who was pointed out by many as the next Mrs. de la Renta) -- and they care a lot about the way they look. It was clear they liked de la Renta's figure-flattering designs.

Ralph Lauren is another designer who is tuned in to his customers. There were no recognizable stars in the audience at his show at the Pierre Hotel, but there were plenty of working women wearing his full, long silk skirts, shirts and jackets.

Lauren fans are usually younger than de la Renta followers -- Buckley being an exception, having just bought lots of separates at the new Polo shop on Madison Avenue. But while the memberships of the two designers' fan clubs may be quite different, the clothes they like are remarkably similar.

Both collections are anchored in the 1950s -- a familiar refrain for the de la Renta set, a popular street and disco look for the younger Lauren following. There are big coats, often shaped with belts and flaring skirts, and loads of full, swingy skirts paired with small, close-fitting sweaters or jersey blouses. There are twin sweater sets, too -- though not worn buttoned up the back, as in the '50s -- and both designers showed turtlenecks, belted waistlines and dolman sleeves.

And yet the two collections are very different, very faithful to the women who like each label.

Lauren offers new colors and fabrics in his classy classics for those who want to add to their collections. There's a new shirt with a big satin bow in black or burgundy, and a new full circle skirt in paisley-printed charmeuse to wear with old Lauren jackets or new -- perhaps a fitted one belted in reptile, shown with flat reptile slingbacks or pumps.

For evening there are lots of long, lean cashmere jersey dresses with huge matching stoles, including a totally unadorned strapless black sheath.

De la Renta is kinder to his clients. He knows some figures need the disguise of careful draping -- as in his jersey dresses for day, which will surely be a huge success next fall. His long gray cashmere evening dresses are perked up with silver embroidery on top, a good distraction for a not-so-young figure.

He offers some worthy 1950s alternatives, including satin cocktail suits with flyaway coats and beaded blouses, and also knows how to make a pure and simple gown for the client with a near-perfect figure -- such as his black satin-faced silk dress with barely a bit of draping over the back.

One of de la Renta's bestselling spring designs was a full-skirted taffeta gown with navy cashmere sweater top with white collar and cuffs. "Of course it was a huge hit -- it brings out the nostalgia in all of us," said Ellin Saltzman, vice president, fashion director of Saks Fifth Avenue.

Two front-row guests at de la Renta's show were fans, but not clients. Paris designer Azzedine Alaia, dressed in shiny black knit, was in town to help model Alva Chin celebrate her birthday and asked de la Renta to be invited to his show -- Alaia's first American show. Seated next to him was French designer Jacqueline de Ribes, who knew de la Renta when he was designing for Lanvin-Castillo in Paris.

Both designers liked the show. "Very different from Paris, but very interesting," Alaia said afterward.

The vicomtesse de Ribes was more specific. "Oscar makes clothes that are very feminine and very comfortable," she said. "That's really very important -- for women to have clothes they are comfortable in. It is what makes his clothes very American."

Had they been at his show, they would have had the same compliments for Ralph Lauren.