A special panel of three federal judges ruled in 2009 that a reduction in the population of California's crowded prisons was necessary to bring treatment of sick and mentally ill inmates up to constitutionally acceptable standards. Some of the state's 33 adult prisons had housed more than double the number of inmates they were designed to hold. After weighing experts' recommendations, the judges ordered that the statewide average be reduced to 137.5 percent of design capacity. The original deadline for reducing the population to that level was June 30, 2013, but the judges extended the deadline to Dec. 31, 2013.

The judges' authority to order the population reduction was upheld by the U.S. Supreme Court in 2011.

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What was the administration required to file with the federal court last week?

Gov. Jerry Brown's administration was required tell the judges how it planned to meet the Dec. 31, 2013, deadline. It also was required to specifically list the state laws that will have to be changed by the Legislature or by court fiat in order to enact that plan.

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How many inmates were in state prisons when the courts ordered the reduction, how many are there now, and how many will be left under the administration's plan?

There were more than 149,000 inmates in the 33 prisons when the court ordered the state to reduce the population to about 110,000 inmates. The prisons currently hold nearly 119,400 inmates, and the administration estimates the population will fall to about 112,600 inmates by Dec. 31 if all its proposals are enacted. The administration projects it will exceed the court-ordered population threshold by nearly 2,600 inmates.

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What steps has the state taken already to lower its prison population?

In 2009, the state enacted SB18, which allowed inmates to earn more early release credits, changed sentencing laws and encouraged the use of treatment programs as an alternative to incarceration. But the biggest change was the 2011 law known as realignment, which sentences lower-level felons and parole violators to county jail instead of state prison. That resulted in a reduction in the prison population of about 25,000 inmates.

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What types of prisoners will be released early under the governor's latest plan and when will that happen?

The governor proposes to parole elderly offenders who are deemed unlikely to commit new crimes and expand an existing program to parole medically incapacitated inmates. A projected 400 elderly and disabled inmates would be paroled by year's end.

The plan also calls for giving minimum-security inmates two days off their sentences for each day they serve, the same currently given to inmate firefighters. Inmates convicted of serious, violent or second-strike crimes would be ineligible. The proposal would decrease the prison population by a projected 148 inmates by year's end.

Early release credits also would be increased for nonviolent second-strike offenders to reduce the population by another 99 inmates. Currently, second-strikers can earn 20 percent off their time; the proposal would increase that to 34 percent. Second-strikers also would be allowed to earn "milestone completion" credits, which they cannot receive under current law.

The changes would take place once they are approved by lawmakers or ordered by the court.

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What is a "good time credit" and how do inmates earn those?

Inmates earn credit toward their release for each day they serve without creating a disciplinary problem. The state also has created "milestone completion" credits for inmates who take part in education or rehabilitation programs.

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Will these early releases be a threat to public safety?

Critics and the Brown administration say yes, but attorneys representing inmates and some prison experts say no.

The administration crafted its plan to avoid releasing minimum-security and second-strike offenders convicted of violent crimes and refused to propose other measures because it said they would create a danger. The elderly and disabled inmates would be released only if they are deemed not to be a threat.

Notably, the state could be forced to release other offenders with a serious or violent history under another pending provision of the court's order.

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What other steps is the governor proposing?

The plan calls for expanding the capacity of minimum-security firefighting camps to add 1,250 inmate firefighters, leasing space for 1,600 inmates at Alameda and Los Angeles county jails and slowing the return of about 8,400 inmates who are housed in private prisons in three other states. Letting those inmates finish their sentences in the out-of-state prisons is projected to ease crowding in California by a projected 3,569 inmates by year's end. The increases in capacity are projected to cost taxpayers between $110 million and $118 million in the fiscal year that begins July 1, with the cost rising to between $137 million and $157 million next year.

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What role does the Legislature play in approving or denying the administration's plan?

Lawmakers would have to act with urgency legislation, requiring two-thirds majorities, to enact the legal changes in time to have an effect by year's end. Legislative leaders have criticized the administration's plan. But if they refuse to act, the court could waive state law or require the state to release other inmates.

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Why did the governor file his plan last week under protest and what does that mean?

Brown objects to his own plan, calling it dangerous, expensive and unnecessary. He intends to appeal the judges' order, arguing that the state now is providing a constitutional level of health care to physically and mentally ill inmates even at the higher population level.

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Who are the judges deciding the case?

U.S. District Court Judge Lawrence Karlton of Sacramento has been overseeing the Coleman lawsuit, filed on behalf of mentally ill inmates in 1991.

U.S. District Court Judge Thelton Henderson of San Francisco has been overseeing the Plata lawsuit, filed on behalf of physically ill inmates in 2001.

9th U.S. Circuit Court of Appeals Judge Stephen Reinhardt of Los Angeles was appointed to round out the three-judge panel. The panel is required to consider population reduction requests brought on behalf of inmates under the 1996 federal Prison Litigation Reform Act.

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What are the judges' options now?

The judges could waive state laws themselves if state legislators fail to enact the legal changes required by the governor's plan.

They could order the administration to take additional steps beyond the governor's plan to meet the court-ordered population cap.

The judges also could order the state to release "low-risk prisoners" to reach the population cap if the state's other efforts fail. The judges have given the state until late July to develop a list of individual inmates who are deemed unlikely to commit new crimes and otherwise might be candidates for early release. The administration said that list could include serious and violent offenders.

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What is the next step in the court case now that the administration has filed its plan?

The judges have given attorneys representing inmates until May 20 to comment on the governor's plan.

The administration has until May 13 to file a formal notice that it will appeal the judges' decision. It also is expected to ask the federal courts to stay the population cap order while the appeal proceeds.