Americans were victims of about 8.1 million violent crimes last year, a 7 percent drop from 1997 and the lowest number reported since the Justice Department began tracking the figure in 1973.

A report released yesterday called the one-year drop "marginally significant," driven by a small but significant drop in aggravated assault rates.

"From 1997 to 1998, no significant changes in rates of rape or sexual assault, robbery or simple assault occurred," said this year's National Crime Victimization Survey. There were slight declines in robbery and simple assault, but rape and sexual assault actually rose slightly, from 311,000 in 1997 to 333,000 in 1998. Rape and sexual assault were the only two crimes to show an increase.

The general 1998 decline continued a downward trend that began in 1994, the survey said.

Attorney General Janet Reno said there is no one reason for the drop. But she gave Clinton administration policies credit for combining the effects of several strategies.

"It's because of more police officers on the streets, tougher sentences, more prosecutions, better prevention programs, a healthy economy and a new approach to crime fighting that involves a closer working relationship between communities and federal, state and local law enforcement," Reno said.

Republicans have said they are relieved at the decline but warn that crime rates remain unacceptably high. They also have pointed to passage of anti-crime legislation since the GOP took majority control of Congress in 1995.

Yesterday's report said that from 1993 to 1998, rates of violent crime -- rape or sexual assault, robbery, aggravated assault and simple assault -- fell 27 percent, from 50 per 1,000 Americans age 12 or older to 37 per 1,000. "Every major type of crime measured -- rape or sexual assault, robbery, aggravated assault, simple assault, burglary, theft and motor vehicle theft -- decreased significantly between 1993 and 1998," the study said.

The annual survey of American households excludes killings, because it asks individuals about their own experiences.

But the report said preliminary figures released separately by the FBI have shown that the number of murders dropped about 8 percent between 1997 and 1998.

Each year the victimization survey analyzes data on nonfatal violent crimes reported to police and those not reported. In 1998 approximately 43,000 households and 80,000 people age 12 or older were interviewed.

According to the report, attackers used some type of weapon in about one-fourth of violent offenses in 1998. "About 40 percent of robbery victims faced a weapon, as did 9 percent of rape or sexual assault victims," the Justice Department said in a statement. "Eight percent of all violent victimizations were committed by offenders armed with a firearm."

About half of all victims of violent crimes knew their assailants, Justice officials said. More than 70 percent of rape and sexual assault victims knew their attacker; for aggravated assault, the figure was 50 percent.

"Almost half of all violent victimizations and about one-third of all property crimes were reported to police each year from 1993 to 1998," the statement said. "Females and blacks were more likely to report violent crimes than males and whites."

The survey also revealed a 12 percent drop in property crimes -- burglary, motor vehicle theft and household theft -- last year and a 32 percent drop since 1993. Personal thefts, which include pocket picking and purse snatching, remained unchanged.