WASHINGTON — Attorney General Eric H. Holder Jr., who last year declared a crisis in America’s legal-defense system for the poor, is supporting a class-action lawsuit that accuses Gov. Andrew M. Cuomo and the State of New York of perpetuating a system that violates the rights of people who cannot afford to hire lawyers.

The lawsuit claims that public defenders in New York are so overworked and overmatched that poor people essentially receive no legal defense at all. It describes a system in which indigent defendants navigate courts nearly alone, relying on spotty advice from lawyers who do not have the time or money to investigate their cases or advise them properly.

Because of substandard legal aid, children are taken from their parents, defendants in minor cases are jailed for long periods and people are imprisoned for crimes for which they might have been acquitted, the civil rights lawyers who filed the suit said.

Although the United States is not a party to the case, Mr. Holder is using the same core legal arguments as the plaintiffs and the weight of the federal government to resolve what he sees as deep-seated unfairness in local criminal courts. His views will bring national attention to a case that has mainly been of interest in New York. After Mr. Holder weighed in last year in a similar case in Washington State, the judge strongly rebuked the public-defense systems in two cities there and ordered improvements.