The number of homicides nationwide dropped for the first time in four years in 2004, while other types of violent crime continued the decline that has led to crime rates not seen in decades, according to FBI statistics released yesterday.

The overall number of violent crimes was down 1.2 percent last year. This included drops of 2.4 percent in murders, 3.1 percent in robberies and 0.5 percent in aggravated assaults. The findings mark the first decrease in murders since 2000, when the number declined by less than 0.1 percent.

The only exception was the number of rapes, which rose by 0.8 percent and has climbed for three of the last four years, the FBI said.

Crime rates, which are calculated on the basis of population, were also down for both violent and property-related crimes in 2004, the FBI reported.

The downward trend holds true in the Washington area, with the District and most of its neighboring jurisdictions reporting lower crime numbers in 2004. The number of murders in the District dropped to 198 last year, and the city is on pace to record about the same number this year.

Although the total number of U.S. murders in 2004 -- 16,137 -- was down compared with 2003, there were still 620 more slayings last year than in 2000. The long-term trend is even worse for forcible rape, which is up 5 percent over the same period. The number of hate crimes also rose slightly, the FBI said.

The overall decrease in crime, which began in the 1990s, is attributed in part to the aging of the baby-boomer generation. Younger males are disproportionately responsible for violent offenses, according to criminologists. Some Bush administration officials have also cited increasingly tough sentencing policies that have led to record incarceration levels.

James Alan Fox, a criminologist at Northeastern University in Boston, said the continued decline in reported crimes is particularly notable given a mixed economic climate that often contributes to higher crime rates. But the broader demographics are masking some remaining areas of concern, he said, including growing violence by youth gangs in some metropolitan areas.

"The fact that it's down is even better than it sounds, given the conditions," Fox said. "But hidden within the overall numbers is this problem of youth crime that we can't ignore."

The number of property crimes also continued a decline last year, according to the uniform reports compiled by the FBI. Burglaries were down 0.5 percent, larceny declined 1.1 percent and vehicle thefts dropped by nearly 2 percent.

The FBI report showed that juvenile arrests on drug-use charges increased nearly 23 percent from 1994 to 2003. The study also showed a record number of marijuana-related arrests.

Researcher Julie Tate contributed to this report.