The nation capped a violent decade with 21,500 homicides last year, the FBI reported yesterday. Experts blamed drugs.

The District of Columbia remained the killing capital for a second year, with 434 murders and other non-negligent homicides, according to the FBI's compilation of crime reports from around the country.

That gave the District a rate of 72 slayings per 100,000 people, compared with the national rate of 8.7 per 100,000. The national rate was a 3.6 percent increase over 1988.

Detroit and Atlanta again occupied second and third place for homicides as they did in 1988. Atlanta had the highest overall crime rate for the second year.

Criminologists blame drug trafficking for the rise in murders and assaults that helped make 1989 the most violent year of the decade. Forcible rapes also rose over the decade, although experts say the increase may be partly due to better reporting of such crimes.

"The drug trade is driving the violence," said Richard Bennett, a professor of justice at American University. "Things such as bad debts, territorial disputes. That's what driving a lot of our assaults and homicides."

The homicide rate was higher as the decade opened. The FBI said 10.2 people per 100,000 died of violent crimes in 1980. But the overall violent crime rate set a record in 1989, exceeding the 1980 level by 11.1 percent.

The rate of violent crime in general -- 663.1 incidents per 100,000 population -- increased 4.1 percent from 1988 to 1989.

The biggest increase during the year was in robberies. The rate rose 5.5 percent to 233 robberies per 100,000 population. The rate of forcible rape increased 1.3 percent to 38.1 rapes per 100,000. Aggravated assault went up 3.6 percent to 383.4 attacks per 100,000.

There were more property crimes than in 1980, but the rate was 5.1 percent lower than at the start of the decade.