Gov. Jerry Brown's plan to shift thousands of inmates from state prisons to county jails will have a significant effect on prison overcrowding, but he may need to ask for more time to meet a court-imposed deadline, a new report concludes.

Facing a deadline two years from now to cut inmate populations by 34,000, the state plans to begin shifting inmates to county jails on Oct. 1.

But a report released Friday by the state's nonpartisan Legislative Analyst's Office suggests that corrections officials may not be able to meet the June 27, 2013, deadline but can make a case to the courts that more time is needed.

"Given the dramatic policy changes the Legislature already has approved, we believe the state has a strong case to make to the courts for a grant of more time to implement this complex realignment of responsibilities from the state to counties," the report states.

Corrections officials have not said whether they will seek an extension, but agency spokesman Oscar Hidalgo said the report shows that corrections has "put forward a good-faith effort to comply with the court's order."

He added that new inmate population estimates will be filed with the court in the next 10 days and that until they are compiled it would be "premature" to decide whether an extension is needed.

The LAO report noted that the U.S. Supreme Court virtually invited state officials to ask for more time in an opinion issued in May.

The opinion upheld an order from a federal three-judge panel requiring California to cut inmate populations to improve medical and mental health care in the 33 adult prisons.

The state's prisons currently hold about 144,000 inmates, roughly 180 percent of the capacity for which they were designed.

The three-judge panel ordered the state to cut that population to 137.5 percent of capacity by June 27, 2013. That means state officials must find a way to cut inmate populations by about 34,000.

The governor's plan would achieve that by shifting responsibility for low-level offenders and parole violators from the state to individual counties beginning Oct. 1.

State prison officials estimated in a court filing last month that the realignment plan will reduce inmate populations by 32,000 over the next two years. The LAO noted that reduction would cut the prison population to 141 percent of capacity.

The report quoted the court opinion from May, which said California "may wish to move for modification of the three-judge court's order to extend the deadline for the required reduction to five years."

The LAO did not specify how much of an extension should be sought, but the inmates' attorney said five years is out of the question.

"If they have a thoughtful proposal, I'll consider it," said Donald Specter, director of the Prison Law Office in Berkeley. "That doesn't mean I'll agree to it."

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