In the moist heat of the quiet rural town of Barnesville, Md., nothing moves -- not a person, not a leaf. Then, a mile from the house, it starts: wiry figures crouched into their handlebars, the sun flat against their backs as they grind their bikes up the narrow winding roads. At first there are just a few but soon there are more, a herd of lean, brightly colored animals coming home to pasture. By the time you reach the driveway of the large white Victorian house, they are everywhere, scores of them and then hundreds.

It is Saturday and they are back, riding into Barnesville as they have every summer month for the past 15 years. This invasion of exercisers on fancy bikes occasionally irritates people who live around Trudy and Paul Meissner's house in upper Montgomery County. But Trudy Meissner says, "I've been weird since I came out here," so she figures the neighbors can put up with the 250 or so visitors who appear monthly.

"I was one of the first outsiders here when we moved in 25 years ago," she says. "They said, 'You'll know you're accepted when they call you Trudy.' " She pauses. "They still call me Mrs. Meissner."

So Mrs. and Mr. Meissner continue to risk the disapproval of their neighbors and invite the members of the Potomac Pedalers Touring Club to their home, preparing food for hordes of hungry bikers each time, opening their pool and their garden and their house, essentially adopting this club of 4,000 members in order to repeat over and over what began as a unique act of gratitude.

It all started because Charlie Meissner liked to ride his bike. The Meissners' son, 36, is a good rider, but he is also autistic. Like most people with that mental disorder, he has a tenuous connection with reality and is unable to follow basic rules of safety. Thanks to a friend of the family, the Pedalers let Charlie ride along with them and watched out for him. At the end of the summer his parents held a small party for what was then a small club and everyone had such a good time they decided to do it again.

"It was just the fact that they were so good to Charlie," says Trudy. "People who don't know anything about autistic people, they really turn them off. If you see an autistic person on the street, you just want to run because they're scary. Just the fact that these people were willing to let Charlie ride and to cope with him, we were very grateful."

By the next year, Charlie was no longer riding with the club, having lost interest just as his parents became more involved with the Pedalers. "He likes to be independent," says Trudy. Biking was replaced by history and airplanes in their son's life, but his parents have remained loyal to the bikers. Over the years the Pedalers grew into what club leaders say is the largest bike club in the country, and so each month the Meissners break out increasingly large containers of taco salad and ice cream and homemade pizzas and cookies and home-grown basil and tomatoes and cabbage. They bring out the galvanized tins for ice and set up the seven picnic tables. They put up signs in the halls directing their guests to the bathrooms. And they wait for the bikers to come.

By 11:30 the place is packed with trim people in those biking outfits that look more like tattoos than clothing. They sit in circles on the ground and sweat, then rise to form a long snaking line to lunch. Some neophytes and determined nonconformists wear the shorts and T-shirts and bellies mere mortals are given to, but they are rare. Stand in the middle of the crowd and you would think you had been transported to a planet where obesity and laziness never existed and 72-year-olds who ride 100 miles a week were the norm.

Over the years there have been Barnesville Bash romances and Barnesville Bash marriages. There are babies who attend transported in plastic tubs on wheels pulled by their bicycling parents. Biking has gotten so popular and the crowds so large that some of the old-timers speak with bittersweet nostalgia of the days when you could ride a bike through Washington and count on knowing any other adult bicyclist you met. Now the whole world seems to bike, or at least much of it, and a large percentage of it seems to have descended on Barnesville.

Richard Meinholdt, the Pedalers' chairman, knows the whole Meissner story, but like many members of the club he remains somewhat bewildered by the 15-year-old tradition. "We really don't know why they do it," he says. "They seem to enjoy it. They're extremely generous people who, I think, probably just get a sense of reward or satisfaction out of providing an opportunity for so many people to have an enjoyable time."

He says this, but in his voice there is the amazement of someone who knows he has not quite managed to decipher an essential mystery.

The Hosts

For four hours Paul Meissner is in the yard, organizing and greeting people. A retired government engineer, he is thin and elfin. When asked to point him out, his wife says to look for the man "in a lavender shirt without hair." For the length of the party, his wife is in the house, joined by a dozen club members who have ridden out early on the "helper ride," a tradition inaugurated three years ago to assist with food preparation and cleaning up. The club also reimburses the Meissners for the food, but the labor is donated.

"You know people come and they say, 'Oh, your mother is so loving and warm' and she is," says Scott Meissner, the 32-year-old younger son who is a microbiologist and helps with each Bash. "But you should have seen us 72 hours before. We are all running around and yelling -- 'You didn't get enough heads of lettuce! The forecaster said it's going to rain! Why don't do you do this!' "

Paul says the family "starts building up speed" on the Monday before a Bash and works steadily throughout the week. Yes, he says, it is plenty of work, "but most of the time we'll get recognition at the annual meeting of one sort or another, a plaque or tickets to dinner out. There's an artist in the club and she painted a picture of the cyclists here in the yard and that's a nice keepsake. But I think it's their gratitude and their appreciation that makes it all worthwhile.

"Also, we're a little bit on the modest side and we always feel badly about the things we didn't get done. We always hope to get the place straightened up a little more. It's always a bit in disarray."

Trudy and Paul Meissner moved to this place on behalf of their furniture. Trudy's great-aunt left her niece a collection of shiny, formal Victorian pieces on the stipulation that Trudy not put them in storage. The furniture just did not look right in their Bethesda rambler, so the government engineer and his wife began to hunt for a more suitable home. High prices kept them looking farther and farther from Washington, and when they found the house in Barnesville they stopped their search.

On 1 1/3 acres, the house looks like one more big, comfortable place from the outside, but inside it harbors the dreams of a 19th-century woodworker. The entrance hall is flanked with dark gleaming columns, the floors glisten, the staircase and the windows and the door frames glow with the soft light of old wood. It's all very stately in the two formal rooms where the great-aunt's furniture sits in state. But move on to the rooms where the family clearly lives and the chaotic reality of life reappears. Books, boxes, sheets of music, knickknacks are scattered about, and the rooms have that silently eccentric air of spaces in which much is done and little is ever put away, spaces that didn't know guests were expected.

Over the years the Meissners have made many changes, adding a pool and transforming the barn first into a basketball court for their children and neighbors and now into a garden workshop.

"Personally, I always feel a little bit guilty about having this great big house and all this property and just this small family in it," says Paul. "When we get a bunch of people out here and they appreciate it, we just feel somehow we're able to share this in a meaningful way."

Trudy worries that the name of the party -- the Barnesville Bash -- might suggest some sort of wild cavorting is taking place on her lawn. This is not the case. There is no alcohol, and the cavorting is limited to some bikers hanging upside down from a swing.

"I like it because I know what it's like to be young and lonely," she says of the party. "If you're young and alone in a big city, you're not going to meet people if you're a nice wholesome person. This is a good way for people to meet each other."

And although she would not claim to be young anymore, it's a nice way for her to meet people too. "I have a friend who says, 'Trudy has a terrible need to be needed.' I'm an only child from a small family. I don't have any relatives." And so she adopts people instead. One friend in the club was a foster mother to a teenage girl who helped with the Bashes. When the friend moved away, the Meissners arranged to pick up the girl from her group home for weekend visits. And even though they do not know many of the names of their biking visitors, they hug them like family.

"I feel like I have all these new daughters," Trudy says as one group of women say thank you and leaves.

She is a pragmatic woman who tutors children in the local public schools. Her mouth is set in the firm, competent line of someone who swats at flies with a sure hand and organizes food for 250 as if making lunch for four. In spare moments, she concentrates on shooing away a reporter. "Don't put too much emphasis on us," she says. "We're so boring. Write about the club. We really want the emphasis to be on the Pedalers and wholesome things young people can do in the Washington area."

Then her hand holding the flyswatter snaps in the air. SWAT! Another Bash intruder has been dispatched.

The Bikers

The Meissners are not bikers (Trudy says she prefers pushing her bike up the hill to riding it). But all around them are people devoted to the sport, including one woman renowned in the club for riding more than 10,000 miles last year and owning somewhere between six and nine bikes, all of which have names.

In the crowded kitchen, people in skintight clothes are talking about their beloved hobby. They all agree there are certain truths about bikers.

They are people who know that knees are not infallible. Former runners turn to biking when their joints begin to die.

They are people who like to be outside.

And they are people who like to eat.

"Cyclists basically cycle so they can eat," says architect Jack Marney.

"They're noshers," agrees Trudy.

"It's the same crowd who does cross-country skiing," offers one woman. "And folk dancing."

Some of the -- how to put this kindly? -- less speedy riders wonder if the racing demons who flock to the most challenging rides really get to appreciate the world they ride through. "Do you think they really see nature when they're riding 100 miles an hour," says one woman. "They see it fast."

On Bash Saturdays there are rides organized for both the fast and the less so. Today there were 12 separate rides of different difficulty and distance but many approaches to riding.

"There are two sets of bikers," says John Posniak, a government librarian. "People who go with an inner tube and a quarter. The inner tube is if they get a flat, and a quarter is if it's anything else wrong. Then there are people who are loaded down with equipment. I'm a librarian. I tend to try to be equipped." For example, he has kept the small rear-view mirror attached to his glasses as he prepares lunch, presumably to warn him of any fast-moving tacos approaching from the rear.

By now, most biking observers agree, there are so many bikers that generalizations are nearly impossible. But Shelley Honikman remembers another time.

Honikman was one of the founders of the Potomac Pedalers in 1967. He remembers on one early ride through Georgetown a small girl pointed to the bikers and said, 'Look Mommy! Look at the grownups on bicycles!' " Now grownups on bicycles are no longer a startling sight. "In the old days, when were were a small club, I think bikers were definitely more individualistic," says Honikman, a pre-school teacher. "We've talked about it. I think we tended not to fall in the mainstream. I think we tended not to be conformists."

Now, they may not be conformists, but they've learned the advantages of belonging to at least one large group. "There's safety in numbers," says John Posniak. Bikers, who often feel themselves at the mercy of people in cars, know that they are a more formidable presence in a group. But it is those very numbers that have irritated some of the Meissner's neighbors.

"I guess bikers and drivers view each other with contempt," says Scott Meissner. "Some of my friends are sod, hay and straw farmers. In those big trucks it's hard enough to drive on these winding country roads without bikers being on the road. The bikers love the peace and greenery but the truckers just want to get home to their pools."

Club chairman Richard Meinhold is diplomatic about the subject. "This event is very unpopular with the Meissner's neighbors," he admits. "Barnesville, being the kind of little town out in the country it is, most of the people who live in that kind of setting do so because they want to live in a tranquil, rural area. They aren't that enamored with the town being overrun by strangely dressed people on bicycles."

Mother and Son

Charles Meissner is slight like his parents and looks much younger than his age. In spite of his autism, Charles Meissner was able to attend the local public school and take some college courses at American University. But his autism is obvious nonetheless. Autistic people are disconnected from the emotions and demands of the outside world and are often obsessed with repetitive motions. Standing in the kitchen fussing with one particular strand of hair over and over, Charlie seems lost somewhere within, introducing himself to newly arrived strangers in a mechanical fashion then quickly turning away when they respond. "Right. Right," he says, in a flat, rushed voice.

The large crowd clearly makes him uneasy. He moves through the house quickly, attempting to restore some sort of routine to the day and spending much of the party sitting in a truck.

"It gets real overwhelming for him," says Trudy. "Part of being autistic is your senses get bombarded. It's not that he doesn't like crowds, but he can get lost in the crowds." Later, when she asks him how he likes the Bash, he says only, "Hot in here, huh? Hot around here."

Charles is here just for the weekend, visiting from the group home in which he lives, largely independent from his parents. His fascination with travel and history took him last year to Montana to watch the running of the cattle in Billings and celebrate the hundredth anniversary of the state, a trip arranged in conjunction with a Montana autism society. He has also taken two flying lessons himself. "I don't know much about that and I don't want to," Trudy says, laughing. "There are some things about Charlie I just don't want to know."

She talks about her son's autism with ease, well used by now to explaining the disorder and taking pleasure in whatever accidental humor it offers. Her tales of her son's idiosyncrasies have the tense, slapstick quality of a comedy routine. "Charlie can't eat when water is running or cupboards are open!" she says, as if asking her listener to imagine the contortions and delayed meals to which this can lead. "There can't be any open doors in the entire house or he won't eat!"

She is laughing, but that's what she tries to do.

"If you don't have a sense of humor you don't survive," she says. "I figure you've got two choices in life. You can take things graciously or ungraciously. I think life is a lot easier if you take them graciously. Sometimes you sit down and look at it and you can get pretty upset. So I don't."

The Future

Paul Meissner says he thinks "it might have been a little scary" if his family had realized 15 years ago how it would all turn out, how a couple of hamburgers would lead to lunch for 300, including a number of vegetarian dishes.

"At this point we keep asking ourselves how much longer we'll be able to do this," he says. Both Paul and Trudy, who are in their mid-sixties, speak of approaching age, although neither appears to be slowing down. And taxes on the house continue to rise while their income stays flat.

"You know, when you get to the last trimester of life, you don't make plans," she says. "You don't plant little trees."

As the party winds down, she manages to get out of the kitchen and onto the porch.

"See you here next year, Trudy?" calls out one departing cyclist.

"Who knows year to year where we'll be," she answers. "But even if we have only one floor, we'll still have the Bash."