Dan Stallings's motorcycle could fit easily into the trunk of your car. At 6-foot-1 and 240 pounds, Stallings himself likely could not.

In fact, it might be a bit of a squeeze to get the burly sales representative into the passenger seat of a small sedan. But give Stallings a few hundred meters of racetrack, and a gallon or so of gas, and he will buzz around on his bright-blue miniature motorcycle for hours.

It is called a pocket bike, and until the past few years there were few of them to be found this side of Europe. The miniaturized motorcycles are, however, attracting growing numbers of ordinary folks like Stallings, who seek the adrenaline rush of large motorcycles without the cost and the hassle.

Two racetracks in suburban Washington, in Frederick County and Loudoun County, are becoming major gathering points for pocket bike enthusiasts in the region, and the Washington area has become something of a national hub for enthusiasts of the nascent sport, according to pocket bike race directors and racers across the country.

The spectacle of adults cramming themselves onto motorcycles that stand only 18 inches tall and weigh about 50 pounds brings to mind circus bears on unicycles. The largest of pocket bikers seem to almost envelop their tiny rides, giving the impression that the rider is somehow propelling himself around the racetrack.

The absurdity, Stallings said, is a large part of the attraction.

"The first time I saw one I just couldn't stop laughing," Stallings, 36, said recently between practice runs at Allsports Grand Prix, an indoor go-kart racetrack in the Dulles area of Loudoun County, where he lives. "I had to get one."

Now, Stallings said, he's hooked.

George "Razor" Holsenback, 26, turned from drag-racing cars to pocket bikes a few years ago because he was in a financial pinch, and pocket bikes cost about $2,500 -- a fraction of the cost of large racing motorcycles or cars.

Pocket bikes "are what filled the void," Holsenback said. "Now I'm addicted."

Whether the bikes can grow from a quirky novelty item to a full-fledged motor sport is anyone's guess. The number of pocket bike clubs in the country has grown in the past three years from two or three to more than a dozen.

The sport first gained momentum in the United States on the East Coast, where clubs started blossoming about three years ago. Clubs on the West Coast got a later start, but membership seems to be growing. There are several clubs there, and the West Coast Minimoto Racing Association began competitive races in 2001.

"A few years ago, nobody had a clue what I was talking about when I mentioned pocket bikes," said Amy Kortum, a member of West Coast Minimoto Racing Association and owner of Pacific Pocketbikes, a San Diego-based pocket bike distributor. "There are getting to be a lot more people who have seen them somewhere before."

There are four major pocket bike manufacturers, three of them in Italy. The fourth is in the Czech Republic. The bikes look like scale models of large racing bikes, down to details on the windshields, exhaust pipes and handlebars.

A precise number of pocket bike enthusiasts is hard to track down because many are part of informal groups and because the sport does not yet have well-established national umbrella organizations.

One group, headquartered in the basement of small-business owner Jay Wandalowski's Kensington home, is jockeying to become the national sanctioning body for pocket biking. The Pocketbike Racing Network, which Wandalowski founded last year, aspires to unite pocket biking clubs across the country by standardizing racing procedures and creating a system for determining a national champion.

As the sport has grown, regulations for racing -- the size of the bikes, the classes of racers -- can vary widely from club to club. Wandalowski says the sport will grow more quickly if national standards are established, so race results have equal weight and meaning across the country.

"What we're trying to do is say, 'Down the line, doesn't it make sense to have some standard regulations, an agreed-upon way of racing?' " Wandalowski said.

Pocket bike racing is well-established in Europe, particularly in Italy, where the bikes are known as minimotos. They are also popular in Japan, where the bikes were introduced in the 1970s.

In the United States, they were available briefly in the late '70s and early '80s, then disappeared until the past several years, when American distributors began selling them on the Internet.

"This has existed [in the United States] since the early 1990s, but nobody had put a comprehensive face on it until the past few years, basically legitimizing it as a sport," said Marcelo Oliveira, one of the main pocket bike distributors in the United States, who sells pocket bikes on the Internet from his home in Eatontown, N.J. "Up until recently it had been treated essentially as a novelty."

For someone seeing the bikes for the first time, it can be hard to get past the impression that they belong in a circus or a roadside carnival, rather than a racetrack. Even an ardent enthusiast like Wandalowski admits that they look "absolutely ridiculous."

As a half-dozen pocket bikes buzzed around a winding racetrack in a converted warehouse in Dulles recently, Cory Laws could not help but suppress a chuckle as he watched the riders crammed onto motorcycles not much larger than tricycles, hitting speeds topping 30 mph.

"Those are really silly!" said Laws, 49, a go-kart driver. "I have a daughter . . . and she likes to ride, but she would just laugh at those things."

But he kept watching. And watching. And marveling at the spectacle.

Though he said he is not likely to buy one of the bikes, they clearly made an impression.

That, Wandalowski said, is in some ways as much as the new sport can hope for.

"Everyone is still in the pioneering stages in this sport," Wandalowski said. "But . . . I see that it's going to grow tremendously."

There is some precedent in the United States for widely popular miniature motorized vehicles: go-karts. In the past 30 years, go-karts have become a widespread recreational sport, and the race circuit has become known as a training ground for NASCAR and Indy car drivers; a healthy percentage of the competitors in the Indianapolis 500 each year cut their teeth as children on the go-kart circuit.

Wandalowski would like to see pocket bikes follow that model.

Since the 1970s, karting (among enthusiasts, the sport always starts with a "k") has grown from about 30,000 active karters to about 50,000 now, said Randy Kugler, president and chairman of the World Karting Association, based in North Carolina.

Pocket bike promoters say it will take years, if not decades, for the sport to reach comparable levels of participation; although the number of clubs has grown rapidly in recent years, membership in most clubs remains fairly small at a dozen or so.

In the Washington area, the Capitol Area Pocketbike Racing Association holds races at a go-kart track near Monrovia in Frederick County. It also has started holding races at the indoor Allsports track in Dulles.

Francois Duret, who runs the Allsports Grand Prix track, said the group adds a bit of quirkiness to the track's usual kart races.

But, he said with a bit of mischief in his eyes, "There's just something unnatural about a grown man sitting on one of those."

Tien Nguyen of Fairfax leans into a curve on his tiny motorcycle, known as a pocket bike, at Allsports Grand Prix in Loudoun County. Another racetrack in Frederick County is also a major gathering point for the bikers. One area group is looking to form a national pocket bike association.Pocket bikes stand only 18 inches tall and weigh about 50 pounds. Peter Tran, left, and Nicki Nguyen of Annandale are part of the region's growing community of pocket bike fans.