Short of a stroll down death row, the trip big women dread the most is to the fitting room of the swimsuit department. And why not? Consider the choices facing them there: one-piece numbers with industrial bust cups and matronly skirts, oh-so-skimpy bikinis or formless tanks with too-tight leg bands and a penchant to ride. (Bend over in one of those beauties, and voila! double-decker derriere.)

Agonies like that were a rite of spring that designer Carol Wior, 40, vowed to wrong. During a trip to Hawaii four years ago, she grew weary of watching women in bathing suits, including herself, constantly tugging at bosom and hip lines and trying to suck in their stomachs. "I figured there must be a way to design a suit with an underwire to give support, an elastic liner to stretch around the entire body and hold it in, and to cut the suit so the rear end wouldn't ride up," says Wior (pronounced Weer).

There was, and six months and 75 prototypes later, she discovered it. Wior's creation, called the Slimsuit, consisted of a girdlelike nylon Spandex liner attached to an underwire bra and covered by a stylish outer shell. Not only did it provide the bosom-to-bottom lift that Wior envisioned, but the new lining delivered a surprise bonus as well: It nipped from one-half to three inches off the waist of the wearer. Wior immediately had her design patented.

Slimsuits, which come with a tape measure for before-and-after checking, are now available in more than 3,000 stores nationwide. They range in size from 6 to 46, and the 35 available styles, including blousons, bandeaux and short, saucy, skirted models, are priced from $44 to $69. "This suit will revolutionize the swimwear industry," predicts Joan Kaner, fashion director of Macy's. "It's amazing to see women walk in, put on the suit and walk out transformed." Evelyn Fazio, national swimwear buyer for J.C. Penney, calls the design "my best-seller and my best reorder. We get letters and testimonials from women of all ages."

For Wior, Slimwear's $19 million in expected sales this year will mark the high point of a career that began 17 years ago in the garage of her parents' Arcadia, Calif., home. A self-taught seamstress, Carol worked as a bank secretary during the day but in her free time began producing a line of "little black dresses" that she sold for $20 each and delivered in a converted milk truck. Within five years, her part-time pursuit had become a multimillion-dollar enterprise.

In the meantime, Carol met Bernard Wior, now 60, a divorced father of three and head of a successful Los Angeles-based intimate-apparel firm. After marrying in 1980, they merged their businesses four years later "so we could drive to work together," says Bernie. Slimsuits are now the fastest growing part of the Wior Corporation, a $60-million-a-year business that employs two of Bernie's three children as well as Carol's widowed mother. The couple now share a 5-bedroom Italianate villa in L.A.'s swanky Hancock Park with Niki, 14, Carol's daughter from a short-lived first marriage. They also have a lakeside hacienda in Lake Isabella, Calif., a live-in cook, a boat, a horse and four cars, including Carol's favorite, her 1953 Bentley.

According to Carol, business can only get better. Except for pregnant women, whom the Slimsuit fits too snugly, Wior believes her designs can benefit almost everyone. Women can choose a skirted model or one with higher leg lines "to take the eye away from the thighs," suits with higher armholes "to prevent breast spillage," or with tiers of ruffles to conceal a large bosom or enhance a small one.

So effective are Wior's suits that women have even worn them under their clothes to support aching backs or to flatten unwanted tummies. Ultimately, though, even Slimsuits have their limitations. What can Wior do for chubby men? "I just tell them to go home and do push-ups," she says.

—By Bonnie Johnson, with Suzanne Adelson in Los Angeles