Fashionable France took the waters in the spa town of Eugénie-les-Bains at the turn of the century. Those who know still come here, and now they're finding Bliss, the French Way in a half-timbered farmhouse spa called La Ferme Thermale

The concept of haute slumming is at least as old as Marie Antoinette, who escaped the tediousness of life at Versailles for the calico pleasures of playing milkmaid at the Petit Trianon. While I was taking the waters recently at La Ferme Thermale, a new French spa in a half-timbered farmhouse built with vintage materials and based on an 18th-century design, I couldn't help thinking that the same faux rustic idea was at work there.

An attendant escorted me to the private Imperial room, where a fire had been lit in a Restoration fireplace of Bordeaux stone, under portraits of Napoléon III and Empress Eugénie. A powder of rosemary, thyme, and sage had been diluted in a claw-foot Carrara marble tub. My "scrub brush" was a bouquet of the same herbs. At first, I felt ridiculous rubbing my body with the bouquet, but once I convinced myself that no one was watching, the whole experience became quite luxurious, if scratchy. It was the most original of the treatments I would take over three impossibly indulgent days at La Ferme Thermale, which opened last fall in the southwestern French spa town of Eugénie-les-Bains.

La Ferme Thermale is the brainchild of Christine Guérard, whose husband, Michel, became one of the chief architects of nouvelle cuisine in the early 1970's. Back then he owned Le Pot au Feu, in a Paris suburb, but in 1974 he closed the restaurant to join his wife at the family spa she was managing in Eugénie. In the years since, the Guérards have transformed this drowsy backwater 75 miles northeast of Biarritz into a pastoral fiefdom that has become one of the crucial stops for hedonists from as far as Topeka and Tokyo.

These days, the fiefdom is looking more like a principality. Besides the two spas (La Ferme and the original facility), the Guérards operate three hotels, two restaurants, and a cooking school, all clustered on parkland planted with magnolia, plane, and tulip trees. The couple's enterprises take up so much of Eugénie, it is impossible to imagine the village— which has a single street and is over almost before it begins— without them.

As La Ferme Thermale made its bow, so too was the cloche lifted on yet another reason to visit: a new style of cooking that complements the smooth herb- and mineral-rich cocktail of treatments. While Christine's spa proposes an improbably romantic rural ideal, Michel's Cuisine Minceur Active, served in the main Les Prés restaurant, updates the "lean" but gastronomically sound dishes that earned him the cover of Time magazine in 1976. The Guérards are protecting their investment: both La Ferme Thermale and Cuisine Minceur Active are trademarked.

Henri IV sampled the springs here in the 16th century, but it was Empress Eugénie, wife of Napoléon III, who called attention to the community in a big way. By 1860 she was so intimately associated with the place that it was named in her honor. She was sold on the beautifying and rejuvenating effects of the waters, which are still endorsed by the French health ministry for their powers in treating rheumatism and weight problems. In her wake, fashionable France followed. The sweet, humble village that was erected to accommodate all this feverish interest is largely the one visitors see today. And tiny though it may be, there is everything to make it self-sufficient, from boulangerie-patisserie to bistro, from gas station to news-and-tobacco shop. The delicious minutiae of small-town life in Eugénie are available to anyone who ventures beyond the grand gates of the Guérard compound to buy a lottery ticket, a baguette, or a tube of toothpaste.

But on the Guérards' side of those gates, it's another world. "In designing La Ferme, I sought the polar opposite of the cool, clinical, generic look of many French spas," says Christine Guérard, who loves Victoriana, has the elongated, mournfully compassionate face of an El Greco Madonna, and is never seen without a ribbon tied under her chin. Her appearance and style belie not only her determination but also the originality and timeliness of her ideas.

The curator of the Marquèze folk museum in nearby Sabres advised Christine on the vernacular correctness of La Ferme's design. Its central public space— paved with burnished 17th-century terra-cotta tiles and soaring to a height of more than 20 feet— is known as the airial. Here in France's Landes department the term describes the clearing or courtyard around which hamlets were customarily built, and where tasks such as chopping wood, threshing wheat, and shucking maize were performed. Guérard says her idea was to create an interior airial, where guests could mingle and rest between treatments."I have always thought an airial was such a beautiful expression of community," she says.

Against one wall of the room is a massive Directoire herb cabinet, made in Provence of luminous cherrywood, with all 66 of its original brass-knobbed drawers intact. Yards and yards of the kind of tobacco-colored jacquard that was once used to cover cows in the Landes to keep them warm in winter are draped over a wrought-iron curtain rail that finishes in bull's horns (Madame is a Taurus). The fabric is not the kind you just walk into a shop and buy. Having discovered some of it in the attic of weaver friends in the neighboring Béarn, Guérard told them she didn't care how much she had to buy as long as they agreed to put it back into production.

The table that dominates the airial was cobbled together from a giant ch’teau shutter and an armful of unmilled acacia branches. Dried rose petals, antique pharmacy jars, and classical stone heads are scattered across it. Pre-war copies of Louis XV and Louis XVI sofas and chairs are covered in a chocolate-and-cream toile that makes reference to the Second Empire vogue for awning stripes. They cradle curled-up guests who study the cloudscape through skylights.

No farm was ever like this.

"I wanted to create a comforting haven that doesn't come right out and tell you what we're all about," says Guérard. "As far as I'm concerned, La Ferme could just as easily be a setting for Latin lessons as for massages. If the only thing guests want is a restful moment and a lemon-balm infusion, they are welcome."

While the standard cure at La Ferme lasts six days, with four to five daily treatments chosen from a palette of 11 in consultation with a staff doctor, guests can also opt for a single treatment. But as with Lay's potato chips, it is difficult to stop at just one. And so my resolve only to get my feet wet melted into a desire to try everything La Ferme has to offer— even if the thermal water's natural temperature of 102 degrees was a tad low for me, a spoiled resident of Provence.

The bath "activated" with herbs that I took in the Imperial room best expresses the spa's herbal-mineral philosophy. In a different version, rosebuds and sprigs of lavender, chamomile, and hawthorn float in the water. In another variation, essential oils of lemon, grapefruit, and orange are added to the water, and a sachet for scrubbing is filled with rinds of the same fruit. The only thing missing from this tropical punch is a paper parasol.

I also sampled a massage on a heated, Chinese-inspired marble console in a white-tiled room with a Murano p’te de verre frieze of bows and bay leaves. It was a bit more embarrassing than the scrub bath, but for a different reason: I am never comfortable while naked in the company of strangers. Studying the frieze to take my mind off my nakedness didn't work, so I forced my masseuse into conversation. In another treatment, a clove-oil "shower" was administered through a hole in a stall by an atomizer-wielding attendant. Though I found the procedure silly, that didn't stop me from enjoying it. But the pleasure ceased when four needlelike jets representing 35 pounds of pressure were turned on me from a distance of five feet. I asked the attendant to move back. It still hurt, so I called off the treatment.

People serious about shedding pounds or licking a medical problem combine La Ferme's treatments with Michel Guérard's Cuisine Minceur Active, somehow finding the strength to resist his full-tilt, calories-to-the-wind Cuisine Gourmande dishes, which are also served at Les Prés. Since such strength had deserted me on previous trips to Eugénie, I decided it was time to show a little professional curiosity and order skinny. I discovered that you do not have to be intent on losing weight to appreciate the technical brilliance of Minceur. Salmon shimmers in a lemony gelée with capers; a vegetable risotto of brown Camargue rice whispers faintly of soy sauce and Parmesan. Lemon verbena "ice cream" is garnished with strawberries and raspberries.

Though there was a normal person's portion of rice on my plate, I have to admit that my interest in the risotto flagged. I suspect it would have done so even sooner if I hadn't had a Gourmande meal to look forward to that night, one that would begin with an eggshell filled with morsels of lobster imprisoned in parsley mousse, asparagus tips— and caviar.

When Guérard first hung out his saucepans in Eugénie-les-Bains 23 years ago, he was profoundly disturbed by the food prescribed for people in Eugénie's spa program— symbolized for him by a depressing plate of grated carrots. At the time, he says, no other chef shared his idea of a cuisine that could be kind on the waistline without betraying France's great culinary heritage.

Guérard created such a cuisine by making butter, eggs, cream, and sugar dirty words in the kitchen. For one of his most famous Cuisine Minceur dishes he took those dreaded carrots, zapped them with mushrooms and low-fat cheese and chicken broth, and sent the mixture into the oven in a baba mold. There was only one problem. The chef began to notice that, after lunch, guests were sneaking away to Miremont, a well-known, full-fat tea salon in Biarritz. Guérard's slimming cuisine tasted great but wasn't always sustaining.

Cuisine Minceur Active addresses that problem by applying Guérard's original principles to two foods he had never served on the spa menu before: grains and pulses, such as peas, beans, and lentils. Both are high in hunger-staying fiber and slow-burning carbohydrates. Transferring minerals to food by using Eugénie's thermal waters as a cooking medium is another innovation. Total calories per meal: 410 to 590. "It is now possible to play two hours of tennis after lunch without wilting," says Antoine Pfeiffer, one of the spa's doctors.

Is there anything the guérards haven't thought of at La Ferme Thermale?Works of Lully composed for Louis XIV's water spectacles at Versailles are used as background music. The chic waffled robes used and sold at the spa were co-designed by Christine Guérard and based on Indian army officers' coats. She even designed the chestnut lounges with hand-stitched wool mattresses and sexy Louis XVI legs.

So it was with obvious distress that Mme. Guérard recently observed a guest cracking a walnut beneath her raffia-slippered foot in the airial.

She had thought of everything, it seems, but the nutcrackers.

Famous for its foie gras, Armagnac, and preserved duck and goose, the Landes department is relatively unknown to Americans. To reach Eugénie-les-Bains, fly from Paris to Pau or Biarritz, then rent a car for the remaining distance (35 and 70 miles, respectively). Both drives pass through beautiful landscapes.

In addition to La Ferme Thermale, there are three hotels in Michel and Christine Guérard's complex, which is formally known as Les Prés d'Eugénie. The 18th-century Couvent des Herbes, a former convent, is the most seductive. Its eight rooms are furnished with antique Turkish rugs, Directoire secrétaires, and Louis XVI armoires. The lavish hangings for the canopied beds are stitched in sailcloth and sprigged ProvenÁal cottons. A double for seven nights, including the standard six-day treatment program at La Ferme Thermale plus three Cuisine Minceur Active meals per day for seven days, costs $2,180‚$2,510 per person (rooms alone are $255 per night, double).

The main hotel, Les Prés d'Eugénie, has 35 comfortable but markedly less charming rooms in the same building as the restaurant. There, the same package costs $2,025‚$2,385 (rooms $220 per night, double).

At La Maison Rose, a shuttered mansion with 31 rooms, the package is $1,210‚ $1,330 (rooms $96 per night). Prices are lower because La Maison is not a full-service hotel. A full morning of treatments at La Ferme Thermale costs $125.

Dinner for two at Les Prés, when you order from the Gourmande menu, is $205‚ $260; $110, from the set Cuisine Minceur Active menu. Dinner for two at La Ferme aux Grives, another Guérard restaurant, goes for $65. In November and April, Michel Guérard offers a six-day cooking course called "L'ABC de la Cuisine," in which both Gourmande and Minceur are taught. The cost is $2,550 per person, based on double occupancy, including accommodations at Les Prés and two spa treatments daily. The courses are taught in French.

For reservations at any of the Les Prés d'Eugénie hotels, spas, and restaurants, call 33-5/58-05-05-05, fax 33-5/58-51-10-10.