In a major sweep aimed at stemming the drug flow in Greater Boston, police arrested 20 ­alleged dealers and gang members early Tuesday following a year-long investigation in parts of Charlestown, Everett, and ­Jamaica Plain.

The raids on their residences were swift, catching many suspects asleep. The focal point was the Charlestown Development, a sprawling public housing complex near Charlestown High School.

One apartment, allegedly the residence of defendant Osvaldo Diaz, was strewn with drugs and cash, prosecutors said. Diaz is considered a prime target in the raid, and prosecutors asked for a $200,000 cash bail for him. Judge Franco Gobourne ordered him held on $50,000 cash bail.

Peter Pasciucco, Suffolk County assistant district attorney, called the apartment where Diaz was appre­hended the “center of the drug-distribution operation” and added that another occupant, ­Anthony Villanueva, appears to be wanted in the Dominican Republic on murder charges.

Suffolk District Attorney ­Daniel F. Conley announced Tuesday that other evidence gathered as part of “Operation Tourniquet” led to 86 indictments against five main targets, as well as the 20 ­arrested Tuesday. Four of the key figures are already in custody on a variety of drug charges.

The raids focused on cutting off a widespread cocaine and heroin distribution network tied to organized gang activity. Authorities did not provide a total amount, nor an estimated street value, of the drugs because they said they were still tallying the amounts.

Community activists and residents praised the sweep, the culmination of a yearlong joint investigation by several agencies, including Boston ­police, the FBI, Everett police, and the Boston Housing ­Authority.

“Nobody should have to live in the midst of these drug-dealing criminals,” Ed Grace, chairman of the Charlestown Neighborhood Council’s public safety committee, said in a telephone interview. “The law-abiding residents have been living in fear for too long, so this is great for the community.”

Boston Police Commissioner Edward F. Davis said at an afternoon press conference that the crackdown “sends a clear message that individuals involved in violence have our full attention.”

He said such long-term oper­ations, which employ under­cover officers, are ­intended to get firearms off the streets. “We are basing all of these investigations on targeting people who shoot other people,” Davis said.

John Foley, the assistant special agent in the FBI office in Boston, said, “As a result of today’s arrests, Charlestown is safer now . . . than it was just hours ago.”

The suspects were ­arraigned Tuesday in three different courts, on charges ranging from drug distribution to selling drugs in a school zone.

Ruth Lopez was charged with 14 offenses, ranging from distribution of heroin to conspiracy to violate drug laws.

Lopez, 36, leaned on a wooden partition during her arraignment at Charlestown District Court, tears flowing down her cheeks.

She and another defendant, Rudy Machuca, allegedly sold heroin to a witness cooperating with authorities. The sales, mostly of 5- and 10-gram quantities, were made inside two Carney Court apartments.

Jennifer Sanders, the attorney representing Lopez, said her client has battled drug ­addiction in the past but is ­not guilty of the charges.

Many of the defendants have records that include past drug convictions, according to authorities.

Daniel P. Campbell, who ­also allegedly sold drugs with Lopez, was convicted in 1995 in Suffolk Superior Court of drug distribution and was sentenced in 1997 to five years in prison.

He was also convicted of manufacturing a class B drug in the early 1990s, the prosecutor said. Campbell was ­ordered held on $1,000 cash bail.

In addition to the Charlestown development, some of the suspects live at the ­Bromley-Heath housing ­development in Jamaica Plain.

BHA administrator William McGonagle said the authority will go into Boston Housing Court, seeking to have tenants involved in criminal activity removed from public housing.

“We’re going to evict them,’’ McGonagle said.