America's young are dying at an accelerating rate, smashed up by car accidents, homicide, drugs and suicide. Right? Wrong. Death rates for adolescents and young adults have reached an all-time low.

The startling reversal in recent mortality trends for 15- to 24-year-olds goes unheralded in the popular press, as well as by academics, professionals and policy makers -- perhaps because of an unwillingness to face up to the currently unfashionable idea that planned and concerted action can make a difference. The overall death rate for 15-to 24- year olds, which stood at 106 per 100,000 in 1960, reached a high of 129 in 1969. It began falling fairly steadily during the 1970s, and had dropped to 96 by 1983.

The greatest single cause of mortality in this age group, motor vehicle accidents, peaked in 1969 and again in 1979; it has now dropped below the 1960 rate. Although the media reflect a contrary impression, even adolescent suicide rates have been going down slightly since 1979. Birth rates among school-age girls were at their highest in the 1950s; today they are well below the levels of 1960 and 1970. Every indicator of marijuana and alcohol use is down since 1979.

What caused this turnaround? We are not sure. But we can make educated guesses. Two economic recessions and demographic changes -- fewer young people at the specific ages with the highest accident risks -- may have contributed to reducing auto accident rates. But deliberate social action also played an important part in each of the improved outcomes. Outraged parents, teachers and students established community programs and lobbied for legislative changes to combat drunk driving. The 55-mph speed limit and greater seat-belt use helped. Some school systems have adopted peer counseling, sex education and other programs. The availability of family planning services and legal abortions reduced the number of births to youngsters unprepared for the responsibilities of parenthood. Preschool programs, more accessible health services and new kinds of family support programs have all helped to improve the odds that even high-risk children will grow into healthy and thriving adults.

The good news is that the trends are improving. The bad news is that an abysmally large number of youngsters continue to have poor outcomes, many of which are preventable. International comparisons provide some perspective. They show that young people in the United States still have five times the homicide rate of other industrialized countries. Only Romania and Hungary have higher teen-age fertility rates than the United States.

Many youngsters in our inner cities are still untouched by the forces that have improved the prospects of their more fortunate peers. Young black men remain victims of homicide at five times the rate of whites. Eight percent of 16-to 23-year- olds, including 26 percent of blacks and 20 percent of Hispanics, score so low on achievement tests as to be ineligible for enlistment in the armed forces. And as recently as the end of 1984, 44 percent of young black men were still unemployed.

The picture is also bleak for disadvantaged younger children. The longstanding gap between black and white infant mortality continues and has increased in the past four years, especially in areas hardest hit by economic downturns and service cutbacks. Data assembled by the Child Health Outcomes Project of the University of North Carolina indicate that very young poor and minority children seem to be most vulnerable to current cutbacks in health and social services. Their deteriorating health status today may presage new downturns when they become adolescents.

The dramatic reversal we are witnessing today in the rates of adolescent death and damage makes clear that, as a society, we are not helpless. Carefully designed interventions can, and do, make a difference.