In a classic "smash 'n' grab" robbery, a thief or thieves broke the window of a Harvard Square jewelry store and stole $1,200 in assorted gems Sunday morning, police said.

"We've been here 23 years and this is the first time anything like this has happened," said Dennis Chin, the owner of the store, Craftsman's Corner. "People have tried other ways of breaking in--never successful--but nothing like this."

Chin, 39, said he is considering taking extra security precautions as a result of the robbery. He has moved valuable merchandise out of the window display at 49a Brattle Street during the night and is even considering the possibility of buying metal grates for the store's windows.

Cambridge Police Detective Frank T. Pasquarello said the robbery occurred at around 2:30 a.m. on Sunday. Witnesses saw the thief or thieves drive down Story St. in a red Oldsmobile following the break-in, he said.

Pasquarello said the burglar or burglars took men's and women's watches, sterling silver bracelets and assorted pieces of gold jewelry, among other gems.

The detective said the city police are still investigating the incident.

"It's a damn shame," Chin said, who replaced the broken window on Sunday afternoon. "It's unfortunate, but I think the quality of life in Harvard Square is just going down.... Things like this didn't use to happen."

Mark Levine, the manager of Hill-side Cleaners, which is next door to the jewelry shop, said this weekend's incident did not cause him any extra concern.

"We've had our share of problems in the past--we've been here for 50 years but nothing recently," Levine said. "We have a very good security system: an alarm, motion detectors, you know. We have people's clothes here so we have to be careful."