FEW buildings in the world are as aesthetically challenged as those in the former Soviet Union. And since the gray slabs built for the proletariat are not likely to face a wrecking ball anytime soon, here in the Ukraine the wealthy few are rushing - discreetly - to give their interiors a capital makeover. Inside these egalitarian eyesores, drab is giving way to fab, Lenin to luxury, Socialist Realism to Architectural Digest. The aim is to fence off the squalor of public spaces with Western luxuries or private eccentricities. The term for this phenomenon is remont - apartment renovations - but in practice it's tiled doghouses, spiral staircases, and even the Versailles look, Ukrainian style. To be sure, most Ukrainians still can barely scrape together enough money for wallpaper. But for those with cash, $40,000 will bring a third-world apartment close to first-world standards. More money can buy a fireplace or swimming pool. Entrepreneurs are sparing neither cash nor building codes. ''Any fantasy can be fulfilled,'' says one local architect. She is showing off a current project, a businessman's home. Though the building's facade is grimy, there is nothing shabby about the work going on inside. The bathroom has a mirrored ceiling. The window grates are custom-made to match the shape of furniture. Window frames are destined to hold stained glass. Much of the style was dictated by the businessman's wife. The architect describes the woman's taste as ''a mix of the Versailles stuff she gleaned in Western magazines and the things she has seen in her friends' apartments.'' Like many of her colleagues in the business, the architect prefers to work in anonymity. Her clients insist on secrecy. Private property may have been legalized, but in the corruption-plagued Ukraine, open displays of wealth court trouble. ''They are all afraid, because if it got out that they put $100,000 into renovations, a whole lot of agencies would descend on them tomorrow asking where they got the money,'' says Anna Drapiy, editor of the architecture and construction section at City, a local business weekly. BEHIND closed doors, though, the only limiting factor is the apartment owner's imagination. One gambit is to buy two apartments, one above the other, take down the ceiling, and create a duplex. Bashing walls to carve out extra room is more popular still. Apartments built to the old Soviet planners' standard of about 80-square-feet per person won't easily accommodate a sauna. Often, the unlikely beneficiaries of the new elite's hunger for elbow room are tenants of communal apartments, where several families share a kitchen and bathroom. For instance, the five rooms that will soon house the businessman with a yen for mirrors were previously shared by two families. In order to secure the larger quarters, the man bought each family a separate, smaller apartment elsewhere. Once a large apartment is in hand, most of its guts must be replaced to accommodate the new owner's gadgets. The old water pipes were not meant for a Jacuzzi; the electrical circuits can't deal with central air-conditioning. And some of the inconvenient walls support the ceiling. One owner of a renovations firm says clients usually meet reminders of such limitations with ''a glassy stare'' and insist on getting everything they asked for. So architects improvise by reinforcing arches, while engineers find ways to improve the water pressure, even at the neighbors' expense. In theory, such work requires municipal permits. But few people in the industry bother. ''Inside your own apartment, you are the boss,'' says an architect. Because most renovation projects are launched on a handshake, there are no reliable statistics. But classified ads by carpenters, plasterers, and other workmen crowd Kiev's advertising circulars. In a country where the official gross domestic product declined by 23 percent last year, one industry is clearly on the upswing. Some of the newly rich have outgrown apartments and started building cottages outside the city. But country homes are no threat to the renovations business while potholes outnumber smooth patches on local roads. ''Before, expensive cars were considered a good investment. Now it is the apartments,'' Drapiy says. Ukraine's drive toward capitalism may not be pretty, but it looks so much better through stained glass.