Designer prices too high? Buy the fabric

When Barbara and Bernard Diamond first met in a line at the John F. Kennedy airport in New York, they had little idea their meeting would result in both a happy marriage and a successful business partnership.

''I adored fabrics and he was a couture fashion designer,'' Mrs. Diamond says. ''It was a perfect match.''

Nine years ago, the Diamonds started the Left Bank Fabric Company in Los Angeles, which specializes in fabrics used by European and American clothing designers in their current collections. The store deals exclusively in fine silks, cottons, woolens, and other luxury fabrics.

''A few stores play with the idea. They may have departments devoted to designer-quality fabrics, but none are as intensive as we are,'' says Mr. Diamond, who has designed clothing collections in London, Rome, and Paris.

Mrs. Diamond estimates customers can duplicate designer styles using the same fabrics for about 20 percent of the retail price. (Companies such as Vogue Patterns now carry designer patterns from Ralph Lauren, Calvin Klein, Albert Nipon, and others.) If they use a dressmaker, she says, the cost amounts to about 50 percent of the retail price for the same garment.

Since opening, the Diamonds' first store has grown to four times its original size. Three years ago they opened a second store in Newport Beach.

The Diamonds often work six days a week, while at the same time devoting as much time as they can to their four-year-old son, Dov. They enjoy working as a team, and their business and personal life often overlap.

''It's a great thing altogether,'' says Mr. Diamond. ''I don't know where the boundary between our personal and our business life is - if there is one. It seems to work out extremely well.''

The Diamonds divide the business responsibilities fairly evenly. Both go on buying trips and attend to day-to-day operations at home.

''My strength is the buying. His strength is knowing how to make a business successful,'' says Mrs. Diamond. She first learned about fabrics from her mother , who owns a fabric store outside Washington, D.C. When Mrs. Diamond was 15 years old, she started accompanying her mother on buying trips. ''I started learning the basics of the fabric business from day one,'' she recalls.

The Diamonds buy directly from European fabric manufacturers who supply the couture houses, choosing from the same fabric lines from which the designers choose. Their store carries fabrics used by Yves Saint Laurent, Ungaro, Givenchy , Adolpho, Perry Ellis, Oscar de la Renta, Ralph Lauren, Bill Blass, and other designers. They also buy ''designer releases'' - extra fabric from New York designers who have some yardage left over from their ready-to-wear clothing lines.

''We do not buy anything made for fabric stores. We are interested in the same fabrics couture designers are using,'' says Mrs. Diamond.

Since they don't buy in large quantities, ''we're not in competition with the major couture houses - they have no objection,'' says Mr. Diamond.

Now, many designers themselves constitute a large part of Left Bank's business. The store also supplies costumers who design wardrobes for television shows such as ''Dynasty'' and situation comedies.

In addition to their wealthy clients, Left Bank appeals to career women who cannot afford designer originals but are seeking high-quality fabrics to make their own clothing from designer patterns.

''It took customers a long time to find us. It takes awhile to nurture clients who will return - who appreciate the quality of the product,'' says Mrs. Diamond.

Fabrics start at $12.99 and go as high as $250 per yard. Most of the fabric sold is in the $40-per-yard range. The selection includes silk crepe de Chine from France and Italy, silk chiffons and metallics from France and Switzerland, and woolens from England. The Diamonds also sell menswear fabrics such as worsted woolens and cashmere suitings.

They also operate a mail-order service that now serves members worldwide.

Above all, the Diamonds enjoy the customer contact.

''I happen to love fabric as an art form, but that in isolation doesn't mean a lot,'' says Mrs. Diamond. ''When people respond to the fabrics the same way I do - that's rewarding. I'm on the floor every day, so I can see which of my (buying) decisions were right and which ones were not.

''A lot of our dearest friends are people who walked through the door,'' she adds. ''It's very special. Nine years is a long time to share with people.''