Serious crime in Southern Maryland showed a slight decrease in the first half of 2002, led by a large drop in thefts in Charles and Calvert counties, according to statistics released last week by the Maryland State Police.

But the state figures also showed a dramatic increase in the number of robberies and aggravated assaults, especially in Charles County. And, after posting the state's biggest crime reduction in 2001, St. Mary's County experienced Southern Maryland's biggest increase in that area for the first half of 2002, when serious offenses went up 11.2 percent.

Overall, the number of serious crimes in Southern Maryland dropped by 1.6 percent in the first six months of 2002, when compared with the same period in 2001, according to the statistics, which are the most recent available.

Serious crimes, called "Part One Offenses" by police, include murder, rape, robbery, aggravated assault, burglary, theft and motor vehicle theft. Police agencies supply the information to the state police for its annual Uniform Crime Report.

Calvert County showed a decrease of 9.6 percent, from 813 crimes to 735. Charles had a decrease of 3.5 percent, from 2,240 to 2,161. The 11.2 percent increase in St. Mary's represented a rise from 846 to 941.

There were three homicides in Southern Maryland in the first half of 2002, down from four in the same period of 2001.

Because there is relatively little crime in Southern Maryland, authorities said the slight overall decrease last year was probably a normal fluctuation, not a downward trend. In the past decade, crime has shown consistently small increases as the region changes from a rural enclave of farmers, watermen and local employees to a suburban community of the Washington metropolitan area.

Yet, authorities said, some of the statistics were alarming. For instance, robberies went up 32.5 percent, from 77 in the first part of 2001 to 102 during the same time in 2002. The increase was fueled by crimes in Charles County, where robberies went up from 57 to 74 -- more than twice as many as Calvert and St. Mary's combined.

In response, the sheriff's office patrol division has zeroed in on some Waldorf neighborhoods that crime analysts say are hotbeds for such incidents. And Sheriff Frederick E. Davis (R) said a separate investigative effort to lock up the robbers has shown some success.

For instance, the sheriff's office charged a Leonardtown man last week with robbing a Waldorf Pizza Hut after he was arrested in Anne Arundel County, where he also faces robbery charges, the sheriff's office said. Davis said investigators know who committed many of the robberies but they are trying to track down the perpetrators.

"What you will find is a lot of the same people are robbing a number of places," Davis said. "Once we find them, we can close out more than one case."

The overall crime decreases seen in Charles and Calvert were fueled by big drops in the number of thefts. In Calvert, thefts went down 15 percent, from 477 to 406, and in Charles, they decreased to 1,226 from 1,401.

Sgt. Bobby Jones, a supervisor in the criminal investigations division of the Calvert sheriff's office, cautioned against calling the drop a trend.

"The numbers are not high enough for anything to be called a trend," he said.

All three counties experienced increases in aggravated assault, which usually means an attack with a weapon or by choking. In St. Mary's, a 36 percent increase in such assaults -- from 124 to 169 -- accounted for much of the increase in crime.

In 2001, St. Mary's saw its crime rate drop by 14.9 percent from 2000, the biggest drop in the state. The first half of 2002 also saw small increases in the number of robberies, thefts, stolen cars and rapes in St. Mary's.