Serious crime slowed in both Arlington and Alexandria during the first half of this year, with Arlington experiencing more than 25 percent decreases in robberies, burglaries and auto thefts.

In Alexandria, serious crimes, which include homicide, rape, robbery and aggravated assault, dropped 2.6 percent from January 1 to June 30 compared with the same time last year. Police officials say it was the 13th consecutive quarter in which serious crimes showed a comparative decrease.

"The police department and other city agencies and our citizens are doing a lot of things right," said Alexandria Police Department spokeswoman Amy Bertsch. "When you consider the population of Alexandria has continued to increase and the crime rate has decreased, it means a person in Alexandria today is less likely to be the victim of a crime than any other time in modern police history."

In Arlington, serious crimes decreased 20.4 percent, compared with the same six-month period in 1998.

That decrease includes a 36 percent drop in robberies, which fell from 114 to 73 incidents, fewer than half of the 148 incidents reported during the same period in 1995. The county also saw a 28 percent decrease in burglaries and a 21.7 percent drop in larcenies.

The countywide number of assaults, which include aggravated and simple assaults, dropped 7.6 percent compared with last year.

Officials said the total number of serious crimes reported in all of 1998 was the lowest the county has seen in 15 years, when Arlington had 35,000 fewer residents than the current estimated total of 188,100.

"We're working hard to deal with problems before they become ongoing conditions," said Arlington County Police Chief Edward A. Flynn.

He said a number of factors, including the national downward trend, have combined to lower the county's crime rate. He pointed to his department's efforts to decentralize police operations and make officers geographically accountable for certain communities, partnerships with neighborhood groups and residents, creative problem solving and the increased responsibility given to patrol officers.

"I'm not foolish enough to declare victory," Flynn said. "Nothing is permanent, but we think we're moving in the right direction."

In Alexandria, robberies decreased 25 percent from 96 to 72 incidents during the first half of this year, and burglary is down 34.3 percent from 394 to 259 break-ins. At the same time, aggravated assault increased 4.8 percent.

And although auto theft in Arlington decreased 28 percent, the same crime shot up 18 percent in Alexandria; 380 cars were stolen in the first half of this year compared with 321 thefts during the same period in 1998.

Bertsch attributed part of the increase in Alexandria to thefts at construction sites where workers tend to leave their trucks and vans unattended for long periods of time and sometimes leave then open for easy access to equipment. She said it's often not the cars that thieves are after, but the tools.

"The increase is not something we're happy with," Bertsch said. "And we're targeting resources to hopefully bring a reduction."