A spate of nearly 30 burglaries and attempted burglaries over 10 months in two Arlington neighborhoods has left residents worried and police puzzled.

Arlington County police say one person committed the burglaries, which took place within a seven-block radius in the Westover and Dominion Hills sections of North Arlington, adjacent neighborhoods divided by Rte. 66.

No one has been injured since the burglaries began in October, but neighborhood leaders are worried. David Rorick, the president of the Westover Civic Association, said his organization is beginning a drive to register all streets in the area in the county-sponsored Neighborhood Watch program.

The burglar, who enters houses in the middle of the night through unlocked doors and windows and steals cash from wallets and desk drawers, is probably a neighborhood teen-ager, said Arlington Detective Gay Mercer. "This person knows the area well," she said, adding that police have no suspects.

"You'd be surprised how safe people figure they are," Mercer said. "There is a surprising number of people who don't lock their doors and windows in that area."

The burglar first struck in October, taking cash from three houses in Dominion Hills. During the next six months, the thief broke into at least 15 houses and tried to enter about five more. From $5 to $300 was taken in each burglary, Mercer said.

"At one house, the perpetrator drank two beers out of the refrigerator before he left," she said. "He felt at home."

The burglaries stopped in June, but resumed last week. Three houses were broken into Thursday, and someone tried to break into two more during the weekend.

Two victims of one of last week's burglaries, Lois and Jack Wilson, who live on N. Kentucky Street, lost more than $300. The burglar entered their house through an unlocked front window.

"I always knew it could happen, but you get a little lax when you have such good luck," said Jack Wilson, a guidance counselor at Washington-Lee High School.

"What would happen if one of us was up when he was in the house?" Wilson asked. "That's the scary thing."

"We're afraid someone's going to get shot," said Rorick, the civic association president and a Marine Corps musician. "All indications are that this guy would run away if he ran into someone in a house, but you never know."

Currently, about half the streets in Westover and fewer than half in Dominion Hills belong to the Neighborhood Watch program, in which residents are trained to spot intruders and signs are installed to warn potential burglars away from the neighborhood.

"People leave their doors unlocked -- the perception is that this is a safe area," Rorick said. "That's not completely true anymore."