Kenneth Carnes has competed in 13 marathons in the past year -- in a wheelchair. And the Prince George's County resident is favored to win the double marathon Wheelchair Race of Champions, which on Tuesday will take 10 competitors from Purcellville to Freedom Plaza in downtown Washington.

"The first marathon is a breeze," Carnes said recently from his home in Morningside, a quiet, residential community near Andrews Air Force Base. "Then it's work . . . . At 40 miles you hit a wall, you break down and cry -- yeah, other guys do it too -- and somehow that restores you, and you keep going."

Years ago, Carnes was only going downhill. On April 14, 1974, he broke his back in a semi-pro motorcycle race and was left a paraplegic.

He could not accept his disability, and turned to drugs and alcohol. He was convicted three times for driving under the influence and landed in jail for 22 months for selling drugs to an undercover agent.

"I had to clean up my act or kill myself," said Carnes, who in 1987 joined Alcoholics Anonymous and Narcotics Anonymous.

Carnes eventually returned to his profession as a dental technician, working at several labs in the area. But he found himself tense and troubled in a different way.

"I was given this new life," he said, "but I was treading water, wrapped up real tight with no way to relax. You know, like with a beer after work. I had to find an escape."

Enter wheelchair racing. It caught the public eye in 1975, when Bob Hall became a Boston marathoner and young Vietnam veterans were changing the focus of wheelchair athletics.

Ken Archer, of Bowie, now a close friend of Carnes's, started competing in 1977 and won the wheelchair competition in the Boston Marathon two years later. Archer since has won the Marine Corps Marathon wheelchair race nine times.

By 1987, Carnes was racing. He competes several times a year, increasingly at times well under one hour and 50 minutes. The best marathoners on foot are happy to do two hours, eight minutes.

Since he started, the "Wild Man" of wheelchair racing has become an Olympic hopeful, competing throughout the world and attracting the attention of a Hollywood producer who has made a television documentary on his life. Last year, Carnes won the Marine Corps Marathon wheelchair race.

With a purse of $30,000 and more than 60 sponsors, the Race of Champions is the richest race in a growing circuit of wheelchair competitions that extends overseas. When it begins next week, bicyclists will ride ahead of the racers along parts of the route to warn about rough spots, like the one that upended Carnes last year: He landed on his head. Two flats and a bent wheelchair frame helped relegate him to seventh place.

Bill Fuller, an official at the Grafton School in Berryville, Va., a facility for disabled children that benefited from money raised at last year's race, sees Carnes as a favorite to win this time because the last stretch of the race is hilly, the kind of terrain where the power-riding Wild Man excels.

Carnes's mother, Eloise, explained, "He goes all the way into whatever he's doing. Maybe they call him the Wild Man because he's always willing to risk himself."

In place of standard wheelchairs weighing more than 50 pounds, racers use special vehicles that weigh about 12 pounds. A new titanium model weighs nine pounds and can cost as much as $7,000.

Carnes has not had a flat since March, and he won seven gold medals at the Pan American Games for the Disabled in Venezuela this year.

Of that competition he said, "I had a very positive attitude, I really flew . . . and they had wide turns I could accelerate through instead of shutting down."

Regularly working out 25 miles a day -- usually from Hains Point through Rock Creek Park in the District to Kensington and back -- Carnes is looking toward the 1992 Olympics in Barcelona, where he plans to particpate in exhibitions. Wheelchair racing is not pegged to become an official sport until 1996.

In the meantime, he figures the double marathon is like doing 30,000 push-ups. With heavily taped motocross gloves, Carnes shoves forward from the top of the chair wheels, known as the 12 o'clock position, down to the 7 o'clock position, and keeps fanning it along. Depending on headwinds, hills and other conditions, he periodically will run through 10 power strokes and coast for two.

"Talking breaks up the monotony," Carnes said. "It's comforting to know somebody is with you."

On April 9, Carnes declared himself a professional athlete. Between 60- to 80-hour workweeks at Clinton Dental Lab in Temple Hills and grueling workouts and races, something had to give.

Since then, International Business Machines Corp. has become one of his sponsors, signing him up for a series of talks to employees across the country about how he has overcome his disability. He also has spoken at schools, the CIA and to the Disabled Awareness Program of Howard County.

CBS Television is considering broadcasting the recently completed two-hour film on his life, "Hell on Wheels." But Carnes is far from complacent.

"Five years ago, I was a threat to society and went to prison," he said recently. "Now I'm a role model.

"I look at myself as a pioneer," he added, "and it's time to help others."