Thomas Murphy of Hyattsville, who is paralized and confined to a wheelchair, was disembarking from a Metrobus Thursday when his wheelchair rolled off a specially designed bus lift and sent him sailing headfirst to the sidewalk.

The accident, the first of its kind since Metro installed special lifts for wheelchairs on 150 buses last spring, left Murphy with cuts and bruises but no serious injuries.

"I was shaken up more than anything," the 24-year-old University of Maryland student said yesterday.

Metro spokesman Cody Pfanstiehl said he believes the accident was caused by a mechanical malfunction, but acknowledge that bus drivers may have trouble with the lifts.

"Those lifts are used so seldom that it's impossible for all 3,000 bus drivers to know how to operate them," Pfanstiehl said. "They were all instructed. But if you hadn't used it regularly, you might forget it."

Murphy broke his neck in a diving accident in 1971 and has been paralyzed from the neck down since then. He rides an electric wheelchair and takes the bus to and from school.

On Thursday afternoon he boarded the F4 bus in College Park, using the special lift. According to Wendy Lanxner, a passenger, "It seemed like the driver wasn't familiar with the lift. The man had to tell the driver how to do it."

Fifteen minutes later, as the bus reached the corner of East-West Highway and Riggs Road, Murphy prepared to disembark.

Murphy wheeled his chair onto the lift, which he said yesterday "wasn't sturdy." A safety device, designed to lock the wheels in place, did not operate. Before he knew it, Murphy said, "My wheelchair just rolled right off the lift. I couldn't stop it."

"He sailed right off the platform and landed headfirst on the gravel," Lanxner said. "He hit his head and he was bleeding realy bad. It upset me so much."

Murphy was taken by ambulance to Washington Adventist Hospital where he was treated for abrasions and released.

Murphy, majoring in psychology at the university, has taken the buses with the special lifts since last April. He said the operation of the lift "varies with the driver."

Overall, he said, he would rate the Metro bus "5" on a scale of 1 to 10.

"It has the potential to offer a service to handicapped people," Murphy said yesterday. "But at this point, I don't think you can say it's dependable."

Metro spokesman Pfanstiefl said the bus is now in "sick bay, being operated on" to cure any malfunction.

Murphy's wheelchair survived the fall, execpt for two bent pedals that have been repaired. "I had my little brother bend them back," Murphy said yesterday.