Raising the legal drinking age to 21 has proved more effective in reducing drunken-driving deaths among 19- and 20-year-olds than did the threat of stiff legal penalties for drunken drivers, according to a comparison of the two policies in Tennessee.> Curiously, tougher laws did deter drivers who were older and younger than this age group. But the deterrent effect lasted only a few years.

In a study published in Friday's issue of the Journal of the American Medical Association, researchers at Vanderbilt University School of Medicine and the federal Centers for Disease Control studied the effect of recent changes in Tennessee laws on death rates from automobile accidents in people aged 15 to 21.

Dr. Michael D. Decker, the report's principal author, said the study underscores the importance of recent successful efforts to establish a nationally uniform drinking age of 21, particularly since 19- and 20-year-olds apparently are relatively unswayed by the threat of penalties for drunken driving.

"At that age, you know you're immortal, you know you'll never be caught and you know that all accidents are survivable," he said. "You just think they're talking about someone else."

The study sought to address disagreement among public health experts over the relative effectiveness of laws, publicity and community campaigns in reducing alcohol-related accidents among young people. Auto accidents are responsible for the majority of fatal injuries, and injuries are the leading cause of death in people under 45.

In the study, researchers used changes in automobile accident death rates among various age groups to assess the effect of two Tennessee laws, a 1982 measure that tightened penalties for drunken driving and a 1984 law that raised the legal drinking age from 19 to 21. The study focused on death rates from single-vehicle nighttime accidents, which tend to be higher in younger drivers and are considered an indicator of drunken-driving rates.

For two age groups studied, drivers aged 15 to 18 and drivers aged 21 to 24, they noted dramatic but temporary declines in death rates starting in 1982, when the tougher penalties went into effect. For the older age group, the decline was short-lived, and death rates rose to their original level by early 1984. For the younger drivers, the lowered death rate persisted until 1986 but eventually rose to the pre-1982 level.> In contrast, the death rate among 19- and 20-year-old drivers was unaffected by tightening the penalties for drunken drivers. But in the 28 months after the legal drinking age was raised, the death rate in this age group decreased by 38 percent. Death rates in 15- to 18-year-olds and in 21- to 24-year-olds were unaffected by the change in drinking age.

Following the repeal of Prohibition, 21 was the legal drinking age in all jurisdictions where drinking was allowed until the 1970s. But in that decade, various factors, including the Vietnam War and a 1970 law lowering the voting age to 18, influenced 29 states to lower their legal drinking age.> Decker said his study also suggests that publicity and community campaigns associated with tightening drunken-driving penalties can reduce death rates, particularly among the youngest drivers, but that such effects are transient unless public attention continues to focus on the problem.

"In the high school-age kids, there is a profound effect from the publicity," he said. "They are at the age when they're beginning to make decisions about drinking and driving."