CHICAGO (AP) _ Violence, including car accidents, has become the leading killer of the nation's young people, overwhelming gains of the last 30 years in medicine's war on fatal disease, according to several studies.

Three of four 15- to 24-year-olds who die are victims of violence, according to the studies. Accidents, primarily auto accidents, account for 53.5 percent of the fatalities and remain by far the leading cause of death in the age group.

But homicide deaths among young people have climbed 300 percent in three decades to become the No. 2 killer, and suicide has climbed even faster over the same period, also surpassing disease to become the third-leading cause of death.

''My sense is that the threshold where violent deaths surpassed illness occurred many years ago,'' said Dr. Robert Blum, author of the study published in Friday's Journal of the American Medical Association.

''But what we tried to highlight here is how violence has overwhelmed illness to the point where this age group is the only one whose health status has not improved over the last 30 years ... that now that we've gained some control over organic illness and infectious diseases, we must learn to cope with different, but more preventable causes of death.''

The article by Blum, who is director of the Adolescent Health Program at the University of Minnesota, heads the magazine's theme issue on adolescents and health.

Blum said an analysis of accident figures challenges the notion that accidents are random events, arguing there are ''predisposing familial, social and cultural factors that belie that perspective.''

He noted that auto accidents account for about 60 percent of all young people's accidents, and more than half those who die are found to have blood- alcohol levels above the legal standard for intoxication.

Yet, he added, in one survey after another, adolescents rank automotive safety as a low priority and increasing numbers report drinking and driving.

Accident fatality rates in the general population have declined about 26 percent since 1950, standing at 42.3 deaths per 100,000 population in 1980. But accident rates involving 15- to 24-year-olds have steadily climbed, reaching 61.7 deaths per 100,000 by 1980.

''Increasingly, there is a sense among our youth of disenfranchisement ... a population facing social stress and pressures at an ever-younger age,'' said Blum.

And Blum said the increasing ''juvenilization of poverty'' will further cloud attempts aimed at improving adolescents' health.

''In the next few years, one of every five adolescent will live at or below the poverty level, and this will have a tremendous effect on morbidity and mortality,'' he said. ''Poverty means poor hygiene, more adolescent pregnancy, more substance abuse, higher school dropout rates, more crime. Unless we start dealing with the underlying causes of adolescent health problems, we are simply providing Band-Aids.''

Blum said the scope of the problem is apparent in the staggering numbers of homicides and suicides among adolescents.

The homicide rate in the general population in 1980 was 10.8 per 100,000 population, a 100 percent increase from 1950. But among 15-to 24-year-olds, homicide was the cause in 15.6 deaths per 100,000 people per year. The numbers rose to 72.5 deaths per 100,000 among black males, largely because more blacks fall below the poverty line.

The suicide rate among 15- to 24-year-olds climbed even faster, Blum noted, accounting for 12.3 deaths per 100,000.

That compared with a rate of 11.4 per 100,000 in the general population, but that number climbed only negligibly since 1950 while the rate for the 15- to 24-year-olds more than quadrupled over the same period.

''The pace of living is being sped up. Experiences when I was growing up, that you confronted in your 20s and 30s, now are being forced upon kids of 10,'' said Blum, 39. ''We need to look at what we're doing to kids, given this tremendous pace.''