PHOENIX — A federal appeals court gave the go-ahead today to a class-action lawsuit by inmates in Arizona prisons who allege they and others are being subject to unconstitutional cruel and unusual treatment.

The judges said the three inmates who complained provided detailed allegations of everything from "outright denials of health care'' to improper isolation policies. And they also had information on how spending on certain services dropped by more than a third over a two-year period even as inmate population did not.

They also backed that up with reports from experts — reports the court said the state did not dispute or counter.

But perhaps the most significant point in today's ruling was that there was evidence that the problems cited were not unique to the individual inmates but instead "systemic failures'' in the prison's health care system "that expose all inmates to a substantial risk of serious harm.''

Today's ruling is not a finding that the Department of Corrections acted illegally. But it will force the state agency to show that it is not running the prison system in an unconstitutional fashion rather than simply addressing the specific complaints of a handful of inmates.

Doug Nick, spokesman for the agency, had no immediate comment on the ruling