SACRAMENTO — In a decision that could dramatically reshape California's criminal justice system, a panel of federal judges Tuesday ordered Gov. Arnold Schwarzenegger and state legislators to find ways to cut the prison population by 40,000, or about one-quarter of all inmates.

The ruling was a stark milestone in the years-long saga of two lawsuits charging that California allows inhumane conditions to fester in its prisons because of severe overcrowding. Law-and-order advocates say such cuts would result in inmates being returned to the streets early or being turned over to cash-strapped counties to jail. The Schwarzenegger administration signaled that it would likely appeal the case to the U.S. Supreme Court.