The next time you try to purchase alcohol, you may be handing your ID to an undercover police officer.

According to Superintendent Harold Murphy of the Cambridge Police Department (CPD), "Cops in Shops"--a program designed to reduce underage drinking--places plain-clothes police officers in and around liquor stores to guard against illegal purchases of alcohol.

"You don't know if that person behind the counter is a police officer," Murphy said.

The Cops in Shops program yielded seven arrests during its first weekend, Cambridge License Commission Executive Officer Richard V. Scali said in a press conference Wednesday afternoon.

"Obviously it was a very successful operation this weekend," Scali said, referring to arrests made on Nov. 21 and 22.

The sting operation was conducted at five package stores each evening from 6 to 11 p.m.

"We got quite a cross-section of people," Scali said.

Among the seven people arrested were two Harvard students, detained Nov. 21 at the L'il Peach located at 1105 Mass. Ave. for transporting alcohol and using false identification.

Also on Nov. 21, a 24-year-old man was arrested on a warrant for assault and battery after being stopped for having purchased alcohol for minors who were waiting in a vehicle.

A 14-year-old and a 15-year-old were arrested Nov. 22 outside of Libby's located at 575 Mass. Ave.

The juveniles were charged with transporting alcohol after being handed two 40-ounce malt liquors purchased for them by a 21-year-old that they had solicited to purchase for them.

The 21-year-old was also arrested.

Michael J. Young, owner of Mall Discount Liquors, located at the Fresh Pond Shopping Center, agreed that the Cops in Shops program has been successful.

"It's sending a positive message to all the underage drinkers," he said.

Young said the program is "giving [underage drinkers] reasons to think about making a purchase."

Murphy said the department "will continue this operation until such time as we are satisfied that youth are no longer provided with illegal alcohol procurement and adults [who supply underage drinkers with alcohol] are prosecuted to the fullest extent of the law."