WASHINGTON - Philadelphia's drop in crime this year has been mirrored by declines across the nation, despite high unemployment and a rugged economy, according to preliminary FBI statistics released yesterday.

FBI figures for the first six months of 2009 left experts scratching their heads over why crime has ebbed during this recession, making it different from other economic downturns of the past half-century. Early speculation includes jobless people at home keeping closer watch for thieves, or extra unemployment benefits keeping people from resorting to crime.

Many experts and police officials had expected crime to rise under the pressure of high joblessness, foreclosures and layoffs.

But murder and manslaughter dropped a surprising 10 percent for the first half of the year, according to the FBI's data. In Philadelphia, the homicide rate during the first six months of the year dropped 11 percent, from 161 to 143.

"That's a remarkable decline, given the economic conditions," sociologist Richard Rosenfeld said of the national decrease. He studies crime trends at the University of Missouri-St. Louis.

Rosenfeld said he didn't expect the 10 percent drop in killings to be sustained over the entire year, as more data is reported. As of yesterday, Philadelphia had logged 296 homicides, compared with 321 the year before, a 7.7 percent decline.

But Rosenfeld said the broad declines are exceptional, given that past recessions have boosted crime rates dating back to the 1950s.

The professor said there are several possible explanations, including that the extended unemployment benefits and other government attempts at economic stimulus "have cushioned and delayed for many people the big blows that come from a recession."

Those benefits will run out eventually, he cautioned.

Another possible factor is that with more people home from work, it is harder for burglars to break into a home or apartment unnoticed by neighbors, he said. Rosenfeld also noted that because big cities tend to have an outsize impact on crime statistics, those cities' new "smart policing" efforts are still working to drive down rates.

"What you see are the large cities - Chicago, Los Angeles, New York in particular - are down considerably, and those large cities are driving the overall change," he said.

On the national level, violent crimes fell by 4.4 percent and property crimes dropped by 6.1 percent, according to the data collected by the FBI. Crime rates haven't been this low since the 1960s, and are nowhere near the peak reached in the early 1990s.

Philadelphia's violent crime figures closely followed the national trend; overall, the rate dropped five 5 percent, including a 10 percent decrease in rapes and a 2 percent drop in robbery.

Philadelphia's decline in property crime outpaced the national averages with a 13 percent drop, led by a 26.6 percent decrease in auto thefts and a 16.8 percent decrease in burglaries.

The FBI figures also show car thefts down nearly 19 percent nationally, continuing a sharp downward trend in that category. Some believe that fewer car thefts reflect the use of new security locking systems installed on most models, as well as more high-tech deterrents like global positioning systems.

The figures are based on data supplied to the FBI by more than 11,700 police and law enforcement agencies. They compare reported crimes in the first six months of this year to the first six months of last year.

The early 2009 data suggests the cutback in crime seen in 2008 is not just continuing but accelerating. In that year, the same data showed a nearly 4 percent drop in murder and manslaughter, and an overall drop in violent crime of 1.9 percent from 2007 to 2008.

According to the FBI figures, reports of violent crime fell about 7 percent in cities with 1 million or more people. But in towns with 10,000 to 25,000 people, violent crime ticked up slightly by 1.7 percent. Each city's data was different, but collectively pointed to less crime in every major category.

Nationwide, rape fell by 3.3 percent, and robbery by 6.5 percent.

Inquirer staff writer Troy Graham contributed to this article.