The move comes after civic groups, scared that several recent killings in those communities could signal a bloody summer, sent a letter to Suffolk County Executive Steve Levy and other local legislators last week.
"We are going to be aggressively investigating and bringing people to justice," police Commissioner Richard Dormer said in an interview Monday.
He added that the department's gang, aggressive driving, and DWI units will be "spending extra time in Brentwood and Central Islip."
In a May 31 letter, a coalition of Brentwood and Central Islip civic groups made several requests of Levy. Among them: an increase in police presence, added federal help, and a law banning gang members from congregating near schools.
In the last two months, at least four people were killed in the two communities. Most recently, a man was killed Sunday at a Brentwood pool hall.
"People are scared," said Ray Mayo, recording secretary for Brentwood Association of Concerned Citizens, one of the groups that wrote the letter. "These gangs are out of control. Something needs to be done. We need someone to step up and stick to it."
Mayo read the letter aloud Thursday to the county legislature's Public Safety Committee. Chairman Jack Eddington (I-Medford) said he sent letters Monday to several law enforcement agencies asking that resources be put into Brentwood and Central Islip.
"I would support anything I can to bring relief to that area and I think the whole committee is behind that," Eddington said.
Through a spokesman, Levy said Monday he has directed police to meet quickly with the groups about their concerns.
Legis. Ricardo Montano (D-Brentwood) said the concerns are "valid" and part of an ongoing push to get help. "Now that the summer is here, we're back to murders, gang shootings, and criminal activity," he said. "The community is demanding a response and they are owed a response and commitment to solve these problems."
Dormer said the community's request to extend working hours of Community Oriented Police Enforcement officers has been somewhat fulfilled: officers, whose shifts end at 11 p.m., now work until 1 a.m. on Fridays and 2 a.m. Saturdays, Dormer said.
Federal authorities helped local officers make arrests leading to convictions, he said.
Dormer called the recent killings "unfortunate upticks" but said overall crime is down 24.7 percent in Brentwood and 9.8 percent in Central Islip compared with this time last year.
Mayo called the increased patrols and officers "good for a quick response" but said residents need long-term solutions, more crimes solved and less deaths in coming weeks.
Anna Torres, executive director of Shepherd's Gate, which runs before- and after-school programs in Brentwood, said, "We have a town that is crying because their children are dying."