The Loudoun County Sheriff's Department is investigating the theft of wallets and purses from 11 houses in the Countryside subdivision in the last month.

Deputies say they believe one person is responsible for the burglaries, which have taken place between midnight and 6 a.m. in occupied houses on Benton, Newland, Webley and Dulaney courts. The deputies say they have no suspect in the cases.

"Our concern is that when a person would be bold enough to break into someone's home knowing that the owners are likely going to be there, then that person has also probably thought about what he will do if cornered," said Lt. Greg Stocks, sheriff's spokesman.

In each case, the losses have amounted to no more than $20 in cash. The burglar has not taken television sets or appliances.

Deputies believe that the burglar looks in through windows and, if he spots a wallet or purse, breaks into the dwelling and makes a quick escape. Some of the houses were unlocked.

In one case, the homeowners encountered the burglar. At 1:30 a.m. Oct. 9, a Webley Court homeowner said his wife awakened to find a man standing in their bedroom near the door. At first she thought the man was her son and called her son's name. When she realized it was not her son, she woke her husband, who chased the intruder. The man fell down the stairs but made his way out of the house through the front door.

"Anything could have happened," said the husband, who asked not to be identified. "Had he been intent on doing bodily harm, we were powerless. It's beyond my comprehension; to go in a house with people in it is crazy."

In the wake of the burglary, the victim said he had bought heat-sensitive lights for the back of his house and plans to buy a security system.

Stocks said the sheriff's office has received several phone calls from residents expressing their concerns and asking for information on the thefts and how to protect their property.

Deputies are urging residents to keep wallets and purses from view, to secure all possible entrances and to leave outside lights on all night.

Loudoun County recorded 223 burglaries in 1985 and 233 in 1986.