The average age at which they died was 22.

Since 1976, almost 45,000 Americans have been killed by motorcycle crashes -- mostly young men in the prime of health. Most were not wearing the one item that might have saved their lives: a helmet.

"Wearing a helmet is the most important thing you can do to save your life in a motorcycle accident," said Diane K. Steed, administrator of the National Highway Traffic Safety Administration, the Department of Transportation's traffic safety arm.

Unhelmeted motorcycle riders are three times more likely than helmeted riders to suffer a fatal head injury, Steed said, and twice as likely to suffer a nonfatal head injury.

If every motorcyclist wore a helmet, DOT estimates, between 1,000 and 1,500 lives would be saved each year.

Motorcyclists are especially vulnerable in a crash because there is no buffer between them and another vehicle, or between them and the pavement. Mile for mile, a motorcycle rider is between 10 and 15 times more likely to die in a crash than is an automobile passenger.

"The experienced motorcyclist will tell you it isn't if you crash, it's when you crash,"said Gary Winn, manager of legislative affairs for the American Motorcyclist Association, which favors motorcycle safety training but opposes mandatory helmet laws.

Study after study has shown that helmets reduce the risk of head injuries, which are the leading cause of death in motorcycle crashes. Yet only 19 states require all motorcyclists to wear helmets, compared with 47 states a decade ago.

The history of motorcycle helmet laws in the United States over the past 20 years resembles an S-curve.

Between the beginning of 1966 and the end of 1969, 40 states adopted mandatory helmet laws, and by 1975, helmet use was required of all motorcyclists in 47 states and the District. The only states without helmet laws were California, Illinois and Utah.

In 1975, DOT began efforts to pressure those three states by withholding federal highway funds from them. But before DOT could act, Congress stripped the agency of its authority to withhold highway funds from states without helmet laws.

That took away the states' incentive to require helmet use. Within three years, under intense pressure from a vocal minority of motorcyclists, 27 states either repealed their helmet laws or weakened them so that they covered only motorcyclists under 18. They did so against the advice of a coalition of health and safety organizations including the American Medical Association, the International Association of Chiefs of Police, the National Safety Council and the American College of Emergency Physicians.

During the heyday of helmet-law repeals, while motorcycle registrations rose less than 10 percent, deaths from motorcycle accidents jumped 46 percent, from 3,312 in 1976 to 4,850 in 1979.

Currently, 19 states and the District require helmet use for all motorcycle riders, 24 states require helmet use under a specified age (usually 18) and seven states have no helmet requirement. Virginia requires helmet use for all riders, Maryland for riders under 18.

Louisiana is the only state to reinstate a helmet law after repealing it in the 1970s. In 1982, the first year after re-enactment of the law, fatalities from motorcycle accidents in Louisiana decreased 30 percent despite an increase of 6 percent in motorcycle registrations.

A helmet law took effect in Maryland in mid-1968. Over the next decade, fatalities from motorcycle crashes averaged 40 per year. But in 1980, the first full year after the law was weakened to cover only those under 18, the number of motorcyclists killed in accidents jumped to 98.

About half of the adult motorcyclists in Maryland do not wear helmets, said Ron Lipps, deputy director of the Maryland state DOT's safety division.

Claims by some motorcyclists that helmets can restrict vision and even cause neck injuries are "not supported by any type of research," according to a DOT report to Congress in 1980.

Even those who oppose helmet use laws generally accept that such laws could save lives and reduce the injury toll on the highways. They don't oppose voluntary use of helmets; they oppose laws mandating helmet use. Often they cite the issue of "personal freedom," and some even claim such laws violate the constitution.

As Rep. Bud Shuster (R-Pa.) put it during congressional hearings on the issue in 1975: "In a free country, people have a right to be dumb and do dumb things."

"It's pretty well decided that helmets are good for you," said the American Motorcyclist Association's Winn. The 140,000-member association is the major opponent of mandatory helmet laws.

"Are motorcyclists smart enough to use helmets without a law? Indeed they are," Winn said. But he acknowledged that only about 50 percent of motorcyclists use helmets voluntarily.

As for the other 50 percent who don't wear helmets, he said, they "aren't living in reality."

The best way to prevent accidents and safeguard motorcyclists, Winn said, is through safety training, tougher licensing and warnings about alcohol use. "Helmet laws, if they're on the list at all, ought to be about number 19."

Though those opposed to helmet laws often claim that motorcyclists have a right to risk their own lives, the cost of motorcycle accidents is borne increasingly by the taxpayers. A study by the University of California at Davis found that 72 percent of the hospital costs of injured motorcyclists, averaging $17,704 per case, were paid for by the state.

Taxpapers ultimately foot the bill for other accident-related costs as well, including rehabilitation, unemployment compensation and disability insurance for injured motorcyclists. And by increasing the toll of deaths and injuries, motorcyclists who refuse to wear helmets raise insurance premiums for other policyholders.

The Supreme Court dismissed the "personal freedom" issue in 1972 by upholding a Massachusetts ruling by a three-judge panel that the risk assumed by a helmetless motorcyclist goes far beyond his or her own life and limb.

"From the moment of the injury," the ruling said, "society picks the person up off the highway; delivers him to a municipal hospital and municipal doctors; provides him with unemployment compensation if, after recovery, he cannot replace his lost job; and, if the injury causes permanent disability, may assume the responsibility for his and his family's continued subsistence.

"We do not understand the state of mind that permits [the] plaintiff to think that only he himself is concerned."