Cambridge and state police arrested a dozen people yesterday in the second largest drug bust in the city's history, following an eight-month investigation of heroin and cocaine sales.

The 12, all but one Cambridge residents, were arraigned yesterday in Middlesex Superior Court for several violations of narcotics laws. The police expect to arrest eight more people suspected in the drug sales by tomorrow, Cambridge Police Sgt. Alan Hayes said yesterday.

The group operated primarily in the Central Square area, selling more than $150,000 worth of drugs each month, Hayes said. Undercover police officers had bought drugs from them for the last four months as part of their investigation.

Last Straw

"We feel we've broken the back of the heroin and cocaine traffic in the city of Cambridge," Jack O'Donovan of the state police said yesterday.

"Whoever is using the drugs probably will have to go elsewhere for them. There won't be any around," Hayes said.

Frank Lounsberry, a state police sergeant involved in the investigation, said the arrests will put a "crimp" in local heroin and cocaine traffic.

The Cambridge police initiated the investigation under the direction of Lt. Edwin Petersen. The state district attorney's office assigned a team of state police led by Lt. George McGarity to cooperate in the effort.

Two of the 12 indicted were already in jail and most were well known in the drug circle, Hayes said.

The biggest Cambridge drug bust, involving millions of dollars, occurred last year at the Hayatt Regency Hotel, Hayes said.