Preliminary figures for 1997 from the Federal Bureau of Investigation indicate serious crime fell across the nation for the sixth consecutive year.

• The overall rate of serious crime fell 4 percent last year -- with a 5 percent decline in violent crimes and a 9 percent decrease in murders and robberies.

• Aggravated assault was down 2 percent and rapes fell 1 percent.

• Property crimes declined by 4 percent -- led by an 8 percent drop in arson -- and car thefts dropped 5 percent.

• States in the northeast led the declines in virtually every category.

For some years, experts have been citing several trends to explain the improving numbers: the aging of the population, toughening of sentencing laws and the increasing number of criminals in prison. They are also now including as a factor the nation's healthy economy.