Through the long, cold nights Thursday and Friday, Michael MacNees sat in his Silver Spring store, a .38-caliber revolver close at hand.

MacNees and other merchants in the small, family-owned shops along the 900 block of Ellsworth Drive have been terrorized by repeated break-ins, attempted break-ins and apparently pointless acts of vandalism. Up and down the street, plate-glass windows and car windshields have been shattered.

In exasperation and fear, about 15 of the clerks and store owners have recently formed a group called Proprietors Irked by the Senseless Sabotage of Ellsworth Drive. They have written a letter to Montgomery County Police Chief Bernard Crooke, asking for more police protection in the area. And last week, some of them decided to take turns spending nights in the stores, waiting nervously for the sounds of would-be intruders.

For MacNees, who always thought of himself as liberal, the transition to gun-toting protector of property is disconcerting, but necessary, he said.

"I'm not a gun type," MacNees, 39, said yesterday. "I'm not a big fan of killing people. You get to the point, though, when you're so frustrated and angry that you think you could almost shoot somebody. And I never thought I'd say something like that."

Last Sunday, a vandal, using a lead pipe and a heavy barrel, smashed a 10-by-6-foot window and a smaller one at MacNees' combination thrift-antique store, the Buy Sell Exchange. Police arrested a suspect. It cost almost $2,000 to repair the damage.

Earlier this year, said MacNees, the windshields of a company truck and an employe's car were shattered. Next door at the Solar Plexus, a men's clothing store, windows have been broken every couple of weeks, and sometimes clothing has been stolen. On the corner of Ellsworth and Fenton Place, Jones Opticians recently was broken into for the first time in its 25 years of business.

The merchants are worried not only about their safety, they said, but also about the future of their businesses. Every time they make a report to their insurance agencies the rates go up, and eventually, they fear, they will be forced to close.

"We all exist in a fragile balance between profit and loss. Without more police protection, we may be driven to a sad ending," said the letter to Crooke, who could not be reached for comment yesterday.

Montgomery County police say they are aware of the problems along Ellsworth Drive and elsewhere in downtown Silver Spring and are making special efforts to solve them.

"We've had special assignment teams -- patrol officers on a plainclothes detail -- working those areas for quite some time," Cpl. Phillip Caswell said yesterday. He declined to say how many officers are involved.

"There's a lot of what we call smash-and-grab crime around there," he said. "But we have been concentrating in the area, and we've made numerous arrests in the last couple of weeks. Last week, we made six or seven arrests like that around downtown Silver Spring in the early morning hours."

Solar Plexus owner Diane Hamou said she is weary of being a crime target and hopes the police will make more of an impact.

"Every time the phone rings at 2 or 3 a.m. we know it's somebody calling to say there's been another break-in," she said. "The other night we were in here late and somebody tried to kick in the back door. We've put bars on the back door, and I hate to put bars on the front door, too, but that seems to be where we're headed."

Hamou said the break-ins have produced a change in attitude, gradual but powerful, among the merchants.

"You get hit so many times you get fed up and your attitude changes," she said. "I used to be lenient, make allowances -- the people who are doing this are poor, they need food on their tables. I don't feel so lenient anymore."

Hamou declined to say whether she keeps a gun in her store. "We do have something on the premises," she said. "When it comes down to it, I don't know what will happen."