Dirt bikes are not soundless, Dennis Stone admits. And the traction from 500 pairs of nobby tires leaves a trail a blind elephant could follow. But don't try to tell Stone that bikers are not tuned in to the environment.

"Heck, when we fall over we put our faces right in the dirt. We clean leaves off the limbs with our teeth," Stone said with a smile. "Sometimes you and the tree actually are one."

Stone, a Defense Department analyst and member of the Northern Virginia Trail Riders, a bikers' club, was in good humor today, good enough to joke about a subject touchier than saddle sores for motorcyclists. Finding enough fenceless terrain to do the kind of racing that a 100-mile competition requires has become a bitter struggle with property owners and environmentalists.

With the mixed blessing of army officials, the Trail riders gained access for the second consecutive year to 76,000-acre Fort A.P. Hill near here to host 500 riders from across the country and an estimated 500 wives, husbands and friends for today's competition. Stone and his companions were as pleased as if they had discovered 40-cent-a-gallon gasoline.

The weather was great, the competition was top caliber -- including six-time U.S. Enduro champion Dick Burleson -- and the course was the kind of wild and wooded countryside that bikers travel as far as 2,000 miles for.

"The run was terrific after my first crash," said 18-year-old Suzy Barr of Alabama, who performed an unplanned double somersault over her handlebars at 30 miles an hour. "If I didn't have this full face gear on my helmet, I wouldn't have a face."

Enduro riders do not venture into the wilderness unprotected. They literally wear a full suit of armor, bound in leather.

"Every guy that's riding competitively has scars and injuries from past battles," said Dick Wirz, owner of a Falls Church refrigeration company and a Trail Riders member. "But Enduro racing is a little more oriented to the older, shall we say wiser, motorcycle competitor. We've mellowed. We're looking to use our heads more than our throttles."

Enduro is not a speed race. Riders are given speed limits and checkpoints to cross, much like auto rallying. Riders lose points for reaching checkpoints either too early or too late.

It is also not a spectator sport.

"If you didn't really love this, it would be terribly boring," said Marti Eppinger standing by a fence in the middle of a thick wood at the one designated spectator spot on the entire course. From her vantage point, the New Jersey native could see her husband, Dave, power up the top half of a steep hill and disappear around a hairpin curve.

"This just makes my life," she said. "I'm going to work full time next year so he can race more."

While not as popular as either dirt or asphalt racing. Enduro has had no trouble attracting fans. What started 15 years ago as jazzed-up trail riding has developed into a sport whose top competitors, though only the top few, can earn more than $70,000 a year for racing. It also has attracted a platoon of participants across the United States whose desire for riding space has sometimes resulted in head-on clashes with environmentalists.

"When you put on an event of 100 miles, you're going through a lot of people's property, on local roads, and getting involved with state and local police," said Wirz. "We're having land problems like everybody else. But it's really hitting motocyclists because of the stigma of the old Hell's Angels."

The Virginia club is delighted with the Army base, which is used as a training ground for troops and as an artillery range. But members fear this may be the last year the Army allows them to hold an Enduro.

"They're making us do things we never had to do before," Wirz said. "They're pulling regulations out of dusty file bins. Many civilians and environmentalists down there don't like motorcyclists. But we're really not hurting anything."

A spokesman for the Army denied the environment was an issue, saying, "There was a considerable amount of paper work involved and that was the main thing. Other than that, everything is fine."