The U.S. Supreme Court on Monday said it will review whether California must cut its prison population by nearly 40,000 inmates to improve medical and mental health care, escalating a legal battle that has been playing out for two decades.

The justices agreed to hear the state's appeal of a court order to reduce its inmate population by December 2011. The state argues that a panel of three federal judges overstepped its authority.

The administration of Gov. Arnold Schwarzenegger acknowledges the state's 33 adult prisons are filled beyond their intended capacity but says it has been making progress to improve health care for inmates. The case involves lawsuits that stretch back to 1990 and include repeated court findings of intolerable prison conditions that violate the Constitution.

At one point, a federal judge said incompetence and malfeasance in California's prison medical system was the cause of one inmate death per week. The prison health care system has operated under the authority of a court-appointed receiver since April 2006.