MIAMI  Public defenders’ offices in at least seven states are refusing to take on new cases or have sued to limit them, citing overwhelming workloads that they say undermine the constitutional right to counsel for the poor.

Public defenders are notoriously overworked, and their turnover is high and their pay low. But now, in the most open revolt by public defenders in memory, many of the government-appointed lawyers say that state budget cuts and rising caseloads have pushed them to the breaking point.

In September, a Florida judge ruled that the public defenders’ office in Miami-Dade County could refuse to represent many of those arrested on lesser felony charges so its lawyers could provide a better defense for other clients. Over the last three years, the average number of felony cases handled by each lawyer in a year has climbed to close to 500, from 367, officials said, and caseloads for lawyers assigned to misdemeanor cases have risen to 2,225, from 1,380.

“Right now a lot of public defenders are starting to stand up and say, ‘No more: We can’t ethically handle this many cases,’ ” said David J. Carroll, director of research for the National Legal Aid and Defender Association.