In May 1979, John McKinley, a construction worker in Akron, Ohio, was thrown over the front of his Honda three-wheeled motorized vehicle as he tried to take a curve and the vehicle rolled over. McKinley, who is now a quadriplegic at age 32, last year won a court award of $2.6 million from Honda.

On April 25, 1984, a 7-year old South Dakota boy died after hitting a fence while driving the same kind of cycle. A month later, a 5-year old boy in Oregon was killed when his three-wheel cycle flipped over, and a 4-year old in Utah died from injuries he received after losing control of the same kind of vehicle on a bridge.

These and hundreds of thousands of other accidents associated with the popular motorized three-wheelers have "increased dramatically," prompting an in-depth investigation by the U.S. Consumer Product Safety Commission staff.

The motorized tricycles, known as "all-terrain vehicles" or ATVs, have jumbo tires, can reach speeds as high as 50 mph and are designed for off-road use on a variety of terrains. Most accidents occur when the ATV hits an obstacle, such as a rock or a ditch and overturns, throwing the rider off, the CPSC said.

"There are too many reports of vehicle instability on the one hand, and loss of rider control on the other, that require us as a regulatory agency mandated to protect the American public to press forward quickly to avert further tragic loss as a result of these facets of the vehicle itself and its design," said CPSC Commission Stuart M. Statler.

The number of injuries last year from the recreational cycles were more than seven times the injuries three years ago, soaring from 8,585 in 1982 to 66,956 in 1984, according to the safety agency. During the same time period, at least 104 deaths were associated with the vehicles, said the CPSC, which added that fatality data is still incomplete and final figures may be double that estimate.

Almost three-fourths of the victims of ATV-related injuries last year were between the ages of 5 and 24 years old, and one-third involved children under 15. Children under 16 seemed to be at the greatest risk attempting to stabilize and control the ATVs while trying to turn, negotiate a hill or avoid an obstacle, the CPSC staff said. Most states allow children to operate such vehicles, at least on private land.

The three-wheelers have the highest percentage of accidents of any recreational vehicle the CPSC has studied. The hospitalization rate for victims of ATV accidents is twice the rate for minibikes and trailbikes and considerably greater than that for snowmobiles, the safety agency said.

Sales of the three-wheel vehicles have increased sharply in recent years, making it the most popular recreational vehicle ever sold, the agency said. From 1980 to 1984, sales of ATVs increased from 136,000 to 650,000. Sales are expected to increase this year to 780,000. At the end of last year, there were more than 1.8 million ATVs in use, according to CPSC estimates.

Four Japanese manufacturers, Honda Motor Co., Yamaha Motor Corp., U.S. Suzuki Motor Corp. and Kawasaki Motors Corp., dominate 95 percent of the ATV market, although an additional 24 firms have begun manufacturing the vehicles.

The manufacturers have said that no problem exists with the ATVs and that most accidents are caused because riders don't follow safety instructions or are careless.

"Education, we believe, is the key to reducing accidents on ATVs," Edward Glynn of American Honda Co. told the CPSC at an October hearing. "We feel most accidents result from riders not following safety instructions."

Statler, responded by asking, "How do you get 4, 5, 6 and 7 year olds to follow these kinds of safety instructions when they have no idea what the degree of risk is?"