BY DAY, they called us mesdemoiselles. There we were in our shorts and T-shirts, savoring croissants, French bread and cafe' au lait at breakfast, stuffing the leftover baguettes into our packs and biking off into the countryside. We went where our moods moved us--to chateaux, cathedrals and dungeons, to abbeys and antique shops, pedaling through vineyards and wheat fields and whole landscapes of sunflowers.

Just before nightfall, we transformed ourselves. Filthy and famished, we checked into the nearest two-star hotel, locked our 10-speeds in the garage, bathed, donned the one dress we each stashed in our packs and set out for a three-star restaurant where--it never failed--they called us mesdames.

This was the vacation my friend Helen and I concocted on a bleak Washington Sunday afternoon last winter. We wanted a trip with all the comforts befitting our station as reasonably well-heeled 30-year-olds, but none of the baggage. No itineraries, no lists of important sights to visit, no binding reservations for hotels, train rides or car rentals. We also wanted all the adventure and serendipity of a college student's trek through Europe, but none of the financial constraints.

"How about bicycling in France?" asked Helen, who on that cold, dreary day hadn't ridden her bike for eight years. "Brilliant!" said I, who hadn't ridden mine in six months.

At the time, neither of us knew how to repair bicycle gears or brakes or even how to change a flat bicycle tire. While we consider ourselves physically fit (we are fair-weather joggers who run up to four miles a day), we had doubts about enduring rides of up to nine hours a day on unfamiliar terrain. We also had visions of our bicycles being stolen or disfigured in transit.

Improbably, everything went our way. Our bikes arrived intact at Orly Airport and never broke down the entire trip. Neither of us suffered exhaustion or serious muscle strain, the weather was unseasonably cool, the sun shined every day, the franc was cheap (8 to the dollar) and the countryside, to our surprise and delight, turned out to be fairly flat.

We traveled 210 miles through the Loire Valley, defined by the Loire, Indre and Vienne rivers, a region of rolling hills but few steep ones.

Only once did we fear we had taken on too much--the first day, which turned into a 24-hour ordeal of dragging two crated bicycles through three airports and two train stations, and at last into the Loire country. From then on, we felt largely prepared for bicycling on unfamiliar turf.

In the weeks before our departure, we took crash courses from friends on how to disassemble our handlebars and pedals for packing (Helen bought a new French bicycle a month before our departure), and how to fix flats and change tire tubes. We added such words as "brakes" and "stuck gears" to our French vocabularies.

We also ignored our athletic friends, who claimed we were not fit enough for the journey. But in a token bow to caution, we scrapped our initial plan to bicycle in Brittany, where the hills are steep and the distance between sights is 40 miles or more. Instead we chose the Loire region, the French chateau country that is so filled with beautiful medieval castles, churches, farmhouses and ruins that we could justify a stop every 10 or 15 miles.

We had plotted our route in advance, using finely detailed Michelin maps that show every dirt road, water tower and windmill as well as the major routes and famous chateaux. We figured we would easily bike 30 miles a day and, consulting the Michelin red guide, selected two-star hotels spaced about that far apart for each night. The hotels accepted reservations by telephone from Washington, with no deposit, so we were free to change plans once en route. This allowed us to ease into a vacation pace.

For the first day, we kept carefully to the routes we had mapped in advance, reaching the chateau at Villandry and its extraordinary formal gardens by midday, and arriving at Langeais, site of a medieval chateau and exquisite tapestries, by early afternoon. We followed a dike road on the south bank of the Loire, appropriately designated by the Michelin map as "picturesque stretch of road." Extending for miles in front of us were lush river valleys, dotted by gray and white stone farmhouses, small churches and every now and then an elegant chateau.

Our hotels were well accustomed to bikers, although most guests arrived in more formidable vehicles. Monsieur and Madame Hosten, proprietors of our hotel in Langeais, welcomed us with a warm, "Bonjour mesdemoiselles, les bicyclistes," when we cycled up to their door in our helmets and sweaty clothing.

They and other hotel managers allowed us to lock our bikes in the hotel garages. The Hostens readily reserved a table for us in their restaurant that night, and introduced us to a specialite' de la Loire: sparkling white Vouvray wine with a touch of strawberry liqueur, served in the hotel's small garden court.

After a day of staying the planned course, we grew eager to explore out-of-the way villages, chateaux and abbeys. As Helen put it, we "got chateaued out." After seeing Azay-le-Rideau, the tiny jewel of a chateau that sits on the Indre River near Langeais, we biked deep into the countryside toward a delicate stone chapel at Champigny-sur-Veude. This tranquil town appeared to draw few tourists, and there were only four other people in the Chapelle St. Louis, marveling alongside us at the magnificent 16th-century Renaissance stained glass windows depicting the life of St. Louis. The windows rival Sainte Chapelle's in Paris.

On the way to Champigny, and from there to Chinon, where Joan of Arc proved her sainthood in 1429, we traveled farm-to-market roads through huge, glorious fields of sunflowers, wheat, corn and grapes. From the crests of hills, the earth resembled a grand, impressionist canvas, so bathed in light that the sun seemed to radiate from inside the sunflowers as well as the sky.

As the hours and days passed, we became adjusted to life at a bicycle's pace, noticing more scents, more tiny chateaux tucked in the hills, more of everything. We decided that bicycling is perhaps the most pleasing speed at which to view the world. In cars, the small wonders along the way are relegated to a blur. On foot, there is almost too much time to look around and, inevitably, to stare at one's feet. But on a bicycle, a clump of pink, white and violet wildflowers blurs just slightly, shimmering like a small work of art.

We soon vowed to avoid highways whenever possible, choosing narrow roads which appear as white lines on the Michelin maps. We were forced onto highways only when we reached major chateaux, such as Loches and Chenonceau.

But even places such as Balzac's chateau in the town of Sache' are reachable on back roads. Balzac retreated to this small estate when his doctor diagnosed him as overworked and in need of "calm and rest," according to the woman who supervises it. In this pastoral setting, Balzac wrote "Pe re Goriot," the great novel of Parisian society, venality and hypocrisy, "The Quest of the Absolute" and "The Lily of the Valley." Inside were some original manuscripts and pictures of the proud novelist and his mistress--later his wife--in a second-floor room overlooking an idyllic valley.

Each day of biking seemed to take us closer to the region, its history and people, ushering us back into the Middle Ages. Consider, for example, Foulques Nerra (987-1040 A.D.), a brooding and brilliant count of the House of Anjou who ruled part of the region starting at the age of 17. He left what seemed to us a schizophrenic legacy, erecting grand Romanesque abbeys and churches in some towns and terrifying dungeons and torture chambers in others. The Michelin guide describes him as at once "ambitious and unscrupulous, criminally violent, greedy and grasping," and prone to "fits of Christian humility and repentance."

We followed Foulques Nerra's trail from Angers to Loches, along the way discovering brocanteurs, the musty shops that deal in objects finer than junk but somewhat less than bona fide antiques. They are found in almost every town in the Loire, and seemed to us to be down-home museums, filled with odd relics of the French past.

Helen bought a turn-of-the-century, white linen dress from a brocanteur located about a mile from the famous medieval chateau in the town of Loches. The shop sits just across the square from a massive Foulques Nerra abbey, and resembles a series of warrens, each holding a different kind of treasure: old plume hats in one room, rusty waffle irons in another, old faience dishes from Brittany in a third, all of them under several coats of dust. We tried on several 19th-century dresses and hats, slipping them over our bike gear and modeling them in front of a warped, old mirror.

The brocante explained to us that the French have a different concept of the terms, Miss and Mrs., than ours. The term mademoiselle is used for all young girls, she said, while madame applies to all grown women, whether married or single. Neither term seemed to apply to us for more than 12 hours at a time. When we were biking or strolling in our shorts, virtually everyone called us mesdemoiselles. When we changed into dresses for our evenings as 30-year-olds, we became mesdames.

At the brocanteur, we spotted a lovely piece of contemporary pottery, and were told that the potter lived only 11 kilometers away, in the tiny village of Chedigny. We biked there to find only one public telephone, a couple of closed bakeries and a small sign pointing up a hill to "region artisanale." There we found the studio of brothers Jean and Claude Luneau.

The main room was decorated with pieces of beautiful hand-painted pottery of every sort--pitchers, platters, plates, bowls, tiles, crocks--in the detailed and floral faience style of 19th-century Brittany, many of them decorated with scenes of hot-air balloons soaring over the Tuilleries or the Loire countryside.

Jean Luneau's beautiful craftsmanship forced us to face the major drawback of bicycling: No extra luggage space for souvenirs. Until then, we had reveled in traveling light. We each packed two panniers, which hooked on the backs of our bicycles, and a pouch that hooked on the front. It took me 10 minutes to pack: three shorts, three T-shirts, one sweater, one pair of blue jeans, a rainproof windbreaker jacket and pants, one polyester dress, one pair of sandals, toilet articles, two spare tire tubes, an allen wrench for reassembling the handlebars, a Swiss army knife, the Michelin green guide to the Loire Valley and a novel.

The heaviest item in my pack was the novel (George Eliot's "Middlemarch," 908 pages). As I was biking up a treacherous hill outside Chinon--the worst we encountered on the week-long trip--I imagined I could feel each of the 710 pages I hadn't read, wishing I had brought a slim volume of poetry instead.

With the help of Jean Luneau, we devised a way around the packing-space obstacle. We selected three plates and two platters--none more than $30, given the favorable exchange rate--which he wrapped lovingly in cardboard boxes. Using elastic straps we had brought for this purpose, we secured the plates on a pletscher rack on the back of my bicycle and headed--carefully--over the hill to Chenonceau.

There, sitting astride the Cher River, was the city's famous castle, one of the most beautiful reminders of the Renaissance. At night, we and hundreds of other tourists strolled the grounds of the floodlit chateau as classical music played over a speaker system. Our bike ride the next day took us through the vineyards outside Chenonceau, where we bought two bottles of wine from an 82-year-old vintner who was the third generation of his family to cultivate grapes in the region.

As cyclists, we were not oddities in the Loire Valley, where women in their 70s casually bicycle about town with baguettes tied to their backs or balanced in their baskets. Between towns, we passed dozens of other bikers, most of them European, and equipped with the same gear we used. We had one accessory, however, that none of our European counterparts had seen: Grab-ons, the black, foam-rubber covers for handlebars, which prevent blisters on the hands. Whenever we locked up our bikes and went for a walk, we returned to find them surrounded by Europeans, squeezing our Grab-ons and discussing them excitedly.

One of the rewards of bicycling all day came at mealtimes, when we felt obliged to stuff ourselves to make up for spent calories. We usually ate a French breakfast of croissants and other breads, and a picnic lunch of fruit and cheese. On hilly days, we were sometimes so hungry that we stopped at a cafe' for a hot lunch--usually an omelette. We gorged ourselves nightly at two- and three-star restaurants, dining on veal kidneys, oyster mousse, rabbit, pigeon, snails and other delicacies, always with wine from the Loire Valley and sinfully rich pastries for dessert. The bill never exceeded $40 for both of us, thanks again to the exchange rate. And neither of us gained a pound.

As the days wore on, we began to fancy that the Loire country had put us under a spell. Otherwise, how could everything keep going our way--the weather, the franc and virtually all chance happenings, including a few close calls with our new pottery, which we packed for the flight home in a nylon carry-on duffel with plenty of padding.

Our first experience back in Washington seemed a signal that the spell of the Loire had lifted. We were met at the airport by a close friend, who offered to carry our bulky duffel through the parking lot. We acquiesced, not thinking to warn that it held our greatest treasures. He then lugged it to his car and dropped it smack on the ground while opening the trunk.

C'est la vie.