SACRAMENTO, Calif. - The U.S. Supreme Court ruled Monday that California must drastically reduce its prison population to relieve severe overcrowding that has exposed inmates to increased violence, disease and death.

The decision, however, doesn't mean the prison gates will swing open in an uncontrolled release.

The high court's decision calls on the state to cut the population to no more than 110,000 inmates, meaning California will have to shed some 33,000 inmates to comply over the next two years. State officials can accomplish that by transferring inmates to local jails or releasing them.

The 5-4 ruling revealed a sharp divide on the court between Justices Anthony Kennedy and Antonin Scalia.

Kennedy wrote for the majority and described dismal conditions where prisoners are denied minimal care and suicidal inmates are held in "telephone-booth sized cages without toilets."

"A prison that deprives prisoners of basic sustenance, including adequate medical care, is incompatible with the concept of human dignity and has no place in civilized society," Kennedy wrote, joined by the court's four Democrat-appointed justices.

Scalia read a blistering dissent from the bench in which he called the ruling "perhaps the most radical injunction issued by a court in our nation's history" and said it would require the release of a "staggering number" of convicted felons.

The ruling also raised concerns among California lawmakers and attorneys general from 18 states who argued that a decision ordering the reduction of California's inmate population infringes on states' rights and could leave their prisons open to similar lawsuits.

It's "a historic attack on the constitutional rights of states and the liberty of all Californians," said former state Sen. George Runner, who had intervened in the lawsuit on behalf of legislative Republicans. It will result in "flooding our neighborhoods with criminals."

California has already been preparing for the ruling, driven as much by persistent multibillion dollar budget deficits as by fears for the well-being of prison inmates and employees. The state has sent inmates to other states. It plans to transfer jurisdiction over others to counties, though the state doesn't have the money to do it.

"Our goal is to not release inmates at all," said Matthew Cate, the state corrections secretary. Shorter term inmates will leave prison before the Supreme Court's deadline expires, and newly sentenced lower-level offenders would go to local jails under the plan.

Concerns over prison crowding and security grew over the weekend with a pair of riots that injured inmates.

A fight by nearly 200 inmates in a San Quentin State Prison dining hall Sunday left four men with stab or slash wounds. On Friday, six inmates were sent to hospitals, two of them with serious injuries, after about 150 inmates rioted at California State Prison, Sacramento.

A special panel of three judges based in different parts of California decided in 2009 to order the prison population reduction. Monday's order puts them in charge of how the state complies. The 2009 ruling grew out of lawsuits alleging unconstitutionally poor care for mentally and physically ill inmates. One case dates back 20 years.

The growth in the prison population in the nation's most populous state can be attributed in part to years of get-tough sentencing laws, including a three-strikes law that sends repeat offenders to prison for life. As of May 11, there were roughly 143,000 inmates in a 33 adult prison-system designed to hold 80,000.

At the peak of overcrowding in 2006, nearly 20,000 inmates were living in makeshift housing in gymnasiums and other common areas, often sleeping in bunks stacked three high. Prison doctors conducted examinations in shower stalls or in makeshift offices without running water, often in full view of other inmates.

One of the federal judges involved in the lower court ruling once blamed the prison system's poor medical care for causing the death of about one inmate every week due to neglect or medical malpractice.

The same judge in 2006 seized control of the prison health care system, putting it under the management of a federal receiver. A second judge in the case has blamed crowding for contributing to poor care for mentally ill inmates, leading some to kill themselves.

At the time, then-Gov. Arnold Schwarzenegger declared a public safety emergency because of the crowding. He then began shipping inmates to private prisons in Arizona, Mississippi and Oklahoma. More than 10,000 California inmates are now housed in private prisons out of state.

"They've made a lot of plans already," said Michael Bien, one of the attorneys who sought the ruling on behalf of mentally and physically ill inmates who suffered in severely crowded conditions. "We're sure it can be done safely and appropriately.

"What's more, it will save a lot of money," he said.

The ruling comes amid efforts in many states, accelerated by budget gaps, to send fewer people to prison in the first place.

Proposals vary by state, but include ways to reduce sentences for lower-level offenders, direct some offenders to alternative sentencing programs and give judges more discretion in sentencing.

"There's a growing consensus that there are better ways to run criminal justice systems," said Michael Mushlin, an expert on prisoners' rights at Pace Law School in White Plains, N.Y.

In recent years, California legislators and Schwarzenegger tried to find ways to reduce prison time for those less likely to commit new crimes. Schwarzenegger signed legislation that increased early release credits and made it more difficult to send ex-convicts back to prison for parole violations. He signed another law that rewards county probation departments for keeping criminals out of state prisons.

One result of those changes is that the state has been able to do away with nearly two-thirds of its makeshift beds, although more than 7,000 inmates remain in temporary housing.

Gov. Jerry Brown sought and signed a bill this year that would reduce the prison population by about 40,000 inmates by transferring jurisdiction for many low-level offenders to counties. The law is stalled until the lawmakers or voters authorize money to pay for the transfer. Much of the money is intended to help counties handle the responsibility of housing convicts.

"As we work to carry out the Court's ruling, I will take all steps necessary to protect public safety," he said in a prepared statement.

Several organizations, from the state prison guards union to the California State Association of Counties, backed Brown's realignment plan - and the elusive funding - as the most practical way to comply with the court's mandate.

"If we don't do it smart, we could have all those people come back for additional crimes," said Chuck Alexander, executive vice president of the California Correctional Peace Officers Association.

Dissenters on the Supreme Court fear the worst, both in terms of public safety and what they described as a lower bar set for court intervention in how state's run their prison systems.

Justice Samuel Alito, in a dissent along with Chief Justice John Roberts, said he feared that the decision, "like prior prisoner release orders, will lead to a grim roster of victims. I hope that I am wrong. In a few years, we will see."

Aside from reducing the inmate population, the court said the state must continue to improve medical treatment in prison. Cate, the corrections secretary, and J. Clark Kelso, the federal receiver who now controls prison medical care, noted that construction of a new centralized medical facility south of the state capital is already under way.

The California dispute is the first high court case that reviewed a prisoner release order under a 1996 federal law that made it much harder for inmates to challenge prison conditions. The law was enacted after Republicans led by Newt Gingrich regained control of Congress and tried to rein in judicial interference in states' affairs, said Frank Zimring, a University of California, Berkeley law professor.

"This is also sort of an object lesson in be careful what you wish for," he said.

Associated Press writer Mark Sherman in Washington, D.C., contributed to this report.