PROVIDENCE –– At dusk, a dozen Providence police officers and state police troopers in unmarked cruisers drove into the back of the Manton Heights housing projects, where the teenage boy killed on Wednesday had lived, and they created a ripple in the neighborhood.

As they got out of their cruisers, wearing identical shirts and their weapons on their hips, and began talking to some of the residents, others watching them began pulling out their cell phones.

Providence police Sgt. Roger Aspinall nodded at them. “You’ll see it. They’ll have their Nextels out. The phones will start ringing.”

The police wanted the residents to know they were there, and make them feel safe. “And for specific targets” –– violent criminals –– “it’s to make them feel uneasy,” said Aspinall.

Last night, without public fanfare, the police quietly launched a new street-crime task force –– made up of city and state police, and agents from the FBI –– with the intention of driving down the violent crime rate in the city’s most troubled neighborhoods.

They’ve been planning this for more than a month, said Col. Dean Esserman, the chief of the Providence police. It was a coincidence that the debut came just two days after the city’s seventh homicide.

Virgilio Rojo, 17, was shot to death as he and a friend walked on Eastwood Street, several blocks away from Manton. The Providence police are investigating his slaying, but had no suspects last night.

“People where these shootings are happening are probably frustrated and they deserve to be safe,” said state police Maj. Steven O’Donnell. “We will put our people into Providence to assist them and curb the violence. And those who want to carry guns and be cowboys, we’ll seek them out.”

The task force is coordinated by Aspinall and state police Lt. Ray Studley, who led the core group of a dozen officers — six city police, six troopers — out into the most crime-ridden neighborhoods last night. They pulled in officers who knew those streets and housing projects best, Aspinall said, and paired them with state troopers.

The police commanders, including Esserman, were also out, though in uniform. They worked the neighborhoods, from Manton to Chad Brown, all the places where violence can be common on sweltering summer nights.

“The homicides haven’t gone up, but violence has increased,” Esserman said by cell phone last night, as he walked on Althea Street. “We’ve been working for the last couple of months to develop every strategy we can. … We are trying to nip the violence before it begins.”

In Manton, some of the officers walked over to a group of women and children sitting in an outside courtyard. One woman watched from her minivan with mixed feelings. “I feel safer when they’re around, but I don’t like to see them harassing people, searching the kids,” said the woman, who didn’t want to be named.

As a state police officer and Providence officer checked three young men in a car, the mother of one of the boys sighed. Her son gave her a sweet smile. He’s always getting pulled over, she said, and he’s a good kid.

The woman, who didn’t want to be named, said she hears gunfire at night. “It’s bad here,” she said, still wearing her blue scrubs from her day shift as a certified nurse’s attendant at Miriam Hospital. “It’s not the drugs. It’s the gunplay.”

amilkovi@projo.com