A fast-moving burglar who dresses in black and steals purses, wallets and other valuables from the homes of people who are fast asleep has struck about 25 times in the Twinbrook area of Rockville since early September, according to Montgomery County police.

Most of the burglaries have been committed in a 100-block area surrounding the Twinbrook Shopping Center, and police say they believe the burglaries are probably the work of one person.

"In almost every case, we have the burglar entering the home through an unlocked window or door and we have him taking mostly wallets and purses containing cash and credit cards," said Officer Vince Iacono, one of two officers investigating the burglaries full time.

"Of course, there is always the possibility that a gang of people are involved, but right now we just don't know."

To date, about $7,000 in cash plus wristwatches, rings and an occasional radio and television have been stolen, Iacono said.

In one burglary early last September, a .25-caliber gun was taken, he added.

In two cases, Iacono said, residents have awakened to see the burglar silhouetted as he dashed through their rooms, snatched purses and sprinted away.

In the most recent incident, last Tuesday, members of a family seated in its living room about 10:30 p.m. were startled by the sound of breaking glass.

They ran outside in time to see a van pulling away. Later it was discovered that an iron automobile jack had been thrown through double glass doors in the rear of their house.

A black cloth purse containing $20, some personal checks, and a Visa credit card were stolen, police said.

The burglar usually strikes between midnight and 6 a.m., according to police.

In Twinbrook, where one 13-year veteran of the Montgomery County police said at least a dozen of his close neighbors are law-enforcement officers, residents are generally heeding police warnings to install stronger locks and to keep windows and doors locked.

"We're being more careful," said Robert Bryan, who works as a printer.

"As neighbors, we try to keep an eye out for each other's houses. You'd think that having all of the cops in the neighborhood would scare off the burglars, but it hasn't."