Legal defense for poor criminal defendants in Suffolk County is getting a significant boost, thanks to settlement of a lawsuit brought by the New York Civil Liberties Union.

The settlement sent $5.4 million to Suffolk, which will allow the Legal Aid Society of Suffolk County and other assigned public defenders to have caseloads and resources more in line with what prosecutors and private attorneys have had.

“It’s going to make a very big difference,” said Laurette Mulry, Legal Aid’s attorney in charge.

For the agency, it will mean reducing caseloads by hiring 23 lawyers to add to its staff of 100. All of those lawyers will work in Legal Aid’s District Court bureau, where some lawyers now handle up to 500 cases a year. The suit said the low quality of defense violated defendants’ constitutional right to adequate counsel.

Another 42 new hires — investigators, interpreters, social workers and support staff — will boost the quality of the work Legal Aid does, Mulry said.

The state made the money available to Suffolk as part of a settlement with the NYCLU, which sued the state over what it called inadequate legal defense for poor people in Suffolk and four upstate counties. In these counties, defense attorneys for the indigent often didn’t meet their clients before their first court appearances, had enormous caseloads and had little access to investigators and others who could help develop defenses in a case.

The money will also allow Suffolk to revamp its assigned counsel program — known as the 18-B program, after the County Law code that governs it. Judges assign such lawyers in murder cases and when conflicts of interest or other issues prevent Legal Aid from representing a defendant.

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Since 1965, the 18-B program has been run on a part-time basis by a volunteer lawyer. For the past 11 years that’s been David Besso of Bay Shore, but $740,000 of the settlement money will allow Suffolk to set up a full-time, more structured office.

The Suffolk Assigned Counsel Program opens Monday with a full-time director, defense attorney Daniel Russo, who ended his Westhampton Beach practice to take the $150,000-a-year job.

Now, when private attorneys are assigned a case under the 18-B program, they have mostly been on their own, Besso said. The new office will change that, giving attorneys who take these cases access to an investigator, an interpreter, a social worker and other support staff to enable these lawyers to provide better representation, he said.

Just as important, he said, will be training for attorneys who take such cases. The program will be able to have veteran attorneys — sometimes Russo himself — watch, critique and help fellow defense attorneys. Prosecutors routinely have supervisors in courtrooms to offer advice. Besso said Russo will be able to be far more involved than he had been.

“He wants everyone to be better,” Besso said. “He cares about the profession.”

Russo said the beefed-up support will deliver not only better training and mentoring for young defense attorneys, but also better results for clients.

Suffolk Administrative Judge C. Randall Hinrichs said that although “there’s never been an issue with the quality of representation of indigent defendants,” the resources now available to Legal Aid and to 18-B lawyers can only help.

Mariko Hirose, senior staff attorney at the NYCLU, said she’s pleased with the steps taken in Suffolk.

“The reforms in Suffolk so far have illustrated what can be done with more money and more access to training,” she said.