When a young black man dies in this country, the most likely cause is not cancer or cardiac arrest or a car wreck.

He is shot to death.

The homicide rate among black men ages 15 to 24 rose by two thirds during the five years ended in 1988, the federal Centers for Disease Control reported this month. Death by gunfire accounted for almost the entire increase, researchers said.

"More and more, guns are becoming the method of choice for killing someone in this age group," said Robert G. Froehlke, a medical epidemiologist in the CDC's Division of Injury Control and the chief author of the report.

The homicide rate is particularly alarming in black male teenagers, the CDC reported. Their homicide rate, already high, nearly doubled between 1984 and 1988 and in some areas exceeds the casualty rate among soldiers in Vietnam, Froehlke said.

Nationally, one of every 1,000 young black males is murdered each year, the report found. No other group in the population even approaches that rate. Homicide accounts for more than 40 percent of deaths in black males between the ages of 15 and 24, and gunshot wounds are the cause of death in 80 percent of those homicides.

In the District and five states -- California, Florida, Michigan, Missouri and New York -- the homicide rate was even higher in 1987, the last year for which complete figures are available.

A total of 463 murders has occurred in the District during 1990 so far, a record for the third straight year. Eighty-two percent were black males.

The latest symbol of the Washington area's carnage is Jay Bias, 20, younger brother of University of Maryland basketball star Len Bias, who died of a cocaine overdose in 1986. Jay Bias was gunned down this month while waiting in his car at a stop sign outside Prince George's Plaza, allegedly by a man who accused Bias of flirting with his wife.

Washington, D.C., is not alone in its soaring homicide rate. FBI crime statistics show that the increase in the homicide rate nationwide has continued at least through mid-1990, with an 8 percent rise in homicides this year. More than a dozen other large U.S. cities -- including New York, Dallas, San Antonio, Phoenix, Memphis, Milwaukee and Boston -- have already marked all-time high homicide totals in 1990. Homicide totals have declined this year in Detroit, Miami, Atlanta and Denver.

The CDC report identified four particularly disturbing aspects of the rising homicide rate in young black men: Gunshots caused more than 80 percent of the deaths and accounted for 96 percent of the recent increase. The rise since 1984 was highest in teenaged black males. The already large gap between the homicide rates of black men and those of other groups is widening. Certain areas, including the District, have extraordinarily high rates.

Homicide was the 10th-leading cause of death in the United States last year. A young black male is six times more likely to be murdered than a young black female, nine times more likely than a young white male and 26 times more likely than a young white female, according to CDC figures for 1988.

Froehlke said it was "outrageous" that homicide was "a significant contributing factor" in the decline in life expectancy for blacks.

The National Center for Health Statistics recently reported a drop in life expectancy for American blacks in 1988, the fourth consecutive annual decline. The drop was large enough to cause life expectancy for the population as a whole to decline slightly for the first time since 1985.

A study reported in the New England Journal of Medicine this year found that black men in the Harlem neighborhood of New York City had less chance of surviving to age 65 than men in Bangladesh. The high homicide rate was the main reason.

The stalled progress in the trend toward longer life spans among Americans signals a recent shift in public health priorities. Death rates from heart disease, stroke and cancer -- historically the biggest killers -- all declined in 1988, but deaths from AIDS and homicide rose substantially.

"People often ask me why, as a physician, I'm dealing with homicide," said CDC's Froehlke, a pediatrician. But he said homicide -- and shootings in particular -- must be considered a public health threat as much as cancer or heart disease.

"If there were a disease responsible for over 40 percent of the deaths of a group of people that should be in peak physical health and it had increased by two thirds in four years, and we knew there was an agent that accounted for 80 percent of those deaths, there would be substantial public health efforts to address that," he said.

What caused the upward spiral in the homicide rate is a complicated question, and what to do about it is even more so. But the first step is a recognition of homicide as a public health crisis, experts agreed.

"We lose nearly 50,000 people a year to homicide and suicide in this country," said Deborah Prothrow-Stith, assistant dean of the Harvard School of Public Health and former Massachusetts health commissioner. "The question is: Where's the beef?

"We need to make violence a public health issue, just like drunk driving, just like heart disease, just like AIDS," said Prothrow-Stith, a physician who has helped develop a curriculum aimed at helping high-school students dispel myths about crime, understand anger and resolve conflicts without resorting to violence.

The rise in the homicide toll, the CDC report noted, results from a set of interrelated factors that include access to firearms, alcohol and drug abuse, drug trafficking, poverty, racism and cultural acceptance of violent behavior. The immediate causes of homicide include domestic violence, child abuse, rape and fighting among acquaintances.

"There aren't any instant solutions," said Frederick P. Rivara, director of the Injury Prevention Center at Harborview Medical Center in Seattle. "If there were, they would have been done a long time ago."

Rivara cited poverty, drug abuse and access to guns as the three key factors in soaring homicide rates. Previous studies have suggested that poor blacks have about the same homicide rate as poor whites, and wealthy blacks about the same rate as wealthy whites, he said.

Another study, reported two years ago in the New England Journal of Medicine, compared homicide rates in Seattle and its Canadian neighbor city, Vancouver, which has a more restrictive gun control policy. Seattle's homicide rate was 60 percent higher than Vancouver's -- a difference accounted for almost entirely by a fivefold greater risk of being shot to death by a person wielding a handgun.

Tougher gun control laws, Rivara said, would help reduce homicide rates for both blacks and whites.

In the District this year, 78 percent of the homicide victims were shot, which is exactly the percentage that the CDC researchers found nationally during the decade from 1978 through 1987.

But a declining percentage of the slayings is classified by police as drug-related. The proportion of killings that are drug-related has fallen from 66 percent in 1988 to 52 percent last year and 39 percent this year, according to D.C. police data.

Despite a common misperception that most homicide victims are killed by unknown assailants during robberies or drug-related crimes, the CDC report said, more than half are killed by people they know.

"Most violence is acquaintance or family violence," said Harvard's Prothrow-Stith. "It starts with an argument. Alcohol plays a role. Owning a gun has something to do with it."

The risk factors are often behavioral, just as in heart disease, and so are the solutions, she said.

"More police won't really help," said Prothrow-Stith. "Criminal justice comes after-the-fact and has very little preventive effect.

"We spend a lot of time trying to change people's behavior to get at heart disease. We have to do the same thing with violence."