Twelve years ago Jim Knaub was a promising 22-year-old pole-vaulter with a 17-foot-7 leap to his credit and Olympic gold on his mind. But he stopped his motorcycle at the wrong California corner one day and automotive mayhem made a visit from behind.

When he came to, he was paralyzed from the waist down for the rest of his life. It took all of six months before he was back at the track, racing.

"As an athlete it was automatic; it was just a matter of figuring out how," Knaub said yesterday as the two-time Boston Marathon wheelchair winner basked in autumn glory after a three-hour push to victory in the 52-mile Wheelchair Race of Champions from Purcellville, Va., to downtown Washington.

Nor is he settling for less than the best in competition now. "I made the finals of the Olympic trials as a pole-vaulter," he said, "but I wouldn't trade an Olympic gold medal or a world-record vault for my experience in wheelchair racing.

"It means so much more," said Knaub, whose victory here won him $6,000 and a silver bowl. "There's no social issue in pole-vaulting. You can show up with a hangover, clear 18-6 and go home with a medal. But as wheelchair athletes, we're always the underdogs. We have the opportunity to motivate people to do things for themselves and for society. There's just no comparison."

That was how Knaub felt when he hoisted his massive torso into a 16-pound, three-wheeled aluminum racing chair at 8:30 a.m., with the tubas and trombones of the Loudoun Valley High School Marching Band tooting a chorus against the distant haze of the Blue Ridge.

That's how he felt when he strapped his withered legs in at the start and pushed away from the pack at the gun, and how he felt for 50-odd miles as he traced the twists and turns of the Washington and Old Dominion Bike Trail through leafy glades barely flaring with the fiery promise of fall.

With a gusty northwester at their backs, he and two top rivals broke away to a lead of more than three minutes over 10 hard-charging rivals at the halfway mark in Herndon.

It was Knaub, 34; muscular, longhaired Kenny Carnes, 33, of Prince George's County, whom Knaub calls "the Maryland Motor," and 32-year-old Doug Kennedy of Haleyville, Ala., forging ahead in a pack, until Kennedy's legs began falling out of their harness with 10 miles to go because a rigging strap on his chair broke.

Forced to slow to tuck his feet in, Kennedy fell back. He was not left behind. "We decided to keep it a threesome," said Knaub. "We didn't want to leave anyone out to dry." He and Carnes eased the pace.

Like bicyclists, wheelchair racers take turns breaking trail for each other and negotiate who takes the lead by shouting inquiries and insults. So it went for Carnes and Knaub, pulling Kennedy along close behind through Arlington, across the Theodore Roosevelt Bridge and into Washington, where small clusters of race fans hooted and cheered them down the final, sun-splashed miles.

Carnes, a local, knew the city and started his sprint 200 yards from the finish on Pennsylvania Avenue before the line ever came into view. Knaub, a newcomer, didn't know where he was and started his sprint when he rounded a bend at 14th Street and the banner appeared, fluttering in the breeze 100 yards away. Kennedy, who figured he had two miles still left to race, was 50 yards back and not a factor.

Down the boulevard of dreams the leaders charged, rivals and brothers, wheel to wheel, huffing like raging buffaloes. Knaub's trip meter said that somewhere in the race he hit 29.5 mph. He couldn't have been going much slower when he charged by Carnes in the last 10 feet to break the tape 29/100ths of a second ahead.

There was a show of sportsmanship as the two pounded each other, but it quickly dissolved into grumbling when the hometown media mobbed Carnes, leaving the winner practically alone. "What is this, the Ken Carnes show?" asked Knaub with mild disbelief. "I thought I won this thing."

Did he ever. His time of 3 hours 1 minute 1.64 seconds knocked more than 48 minutes off Rafael Ibarra's winning time last year in the first Race of Champions. Knaub said the big tailwind and the absence of rain, which plagued the 1989 event, accounted for better time. Ibarra was one of three nonfinishers today, dropping out at Mile 35 with hip pains and chair troubles.

Another nonfinisher, Rose Winand, the only woman invited to compete, criticized race organizers for forcing her out at the halfway mark when she fell more than a half-hour behind the leaders. The 30-minute cutoff was agreed to beforehand, designed to protect the competitors and ease traffic control problems at road crossings, but Winand said it rankled her anyway.

"I was pulled, I didn't quit, and that eats away at you," said the Pennsylvania college student. "As a person in a wheelchair, people are always pulling, pushing at you. You feel you have no control, and I didn't in this case."

It was one of few unpleasantries on an otherwise glorious day. Race chairman Bill Fuller, himself a polio victim who uses crutches to walk and a wheelchair to race at the recreational level, said the event raised more than $250,000 in sponsor donations, principally from the Hardee's fast food chain, whose donation was in six figures. The total marks a tremendous increase over last year's inaugural event, which raised $18,000.

Fuller said after deducting the cost of this race and the four qualifiers held over the summer to pick the invitees here, profits of about $150,000 will go to the Grafton School in Berryville, Va., where he works, and to the Shalom Et Benedictus School in Winchester.

The schools are for youngsters with emotional and physical problems. Teachers at both work to get children back in the mainstream, and many of the youngsters were along the route today, cheering the racers.

Said Kennedy, who wound up third today, a victim of gear breakdown at the worst possible time:

"We don't make excuses. Our focus isn't on disability; it's on ability."

1. Jim Knaub ...... Long Beach, Calif.

2. Ken Carnes .......Morningside, Md.

3. Doug Kennedy .....Haleyville, Ala.