(Adds details from panel's ruling)
By Alex Dobuzinskis
LOS ANGELES, June 20 (Reuters) - A panel of federal judges ordered California on Thursday to ease overcrowding in state prisons by reducing the number of inmates by about 10,000 this year, and criticized in harsh terms what they described as foot-dragging in dealing with the matter.
The three-judge panel also repeated an earlier warning to potentially hold California Governor Jerry Brown in contempt if a reduction plan is not implemented. The governor said he would seek a stay of the ruling.
California, the nation's most populous state, has been under court orders to reduce inmate numbers in its 33-prison system since 2009, when the same three-judge panel ordered it to relieve overcrowding that has caused inadequate medical and mental healthcare.
The issue has become a political football for Brown, partly because reducing the population in state prisons has meant that local jurisdictions have to host some convicts in county jails who previously would have been sent to state prisons.
Earlier this year, the judges rebuffed a request by Brown to vacate the 2009 order. Brown had contended the state had fixed the crowding problem and that further prisoner releases would harm public safety.
"The history of this litigation is of defendants' repeated failure to take the necessary steps to remedy the constitutional violations in its prison system," the judges said in Thursday's ruling.
The three jurists - Stephen Reinhardt, Lawrence K. Karlton and Thelton E. Henderson - said the state's "unwillingness to comply" with a ruling to reduce prison overcrowding requires them "to order additional relief."
The judges said if current efforts to reduce crowding do not result in the state reaching a prison population target of 137.5 percent of capacity by the end of the year, the state must then free prisoners from a list of inmates at low risk of recidivism.
"Failure to take such steps or to report on such steps every two weeks shall constitute an act of contempt," the judges said.
Brown, a Democrat, has said he lacks the authority to enact certain measures to reduce prison crowding. In court papers filed earlier this month, attorneys for the governor said state officials were working on legislation to solve that problem.
The legislation would, among other things, make it easier for inmates to be released on parole for medical reasons and establish a parole process for elderly inmates who are a low risk to the public, the state's court papers said.
Thursday's ruling stemmed from class action litigation accusing the state of failing to provide prisoners with adequate mental and medical healthcare. That led to a 2009 ruling that treatment of inmates in the state's overcrowded prison system violated constitutional protections against cruel and unusual punishment.
In 2011, the U.S. Supreme Court upheld the 2009 order to reduce California's prison population.
Don Specter, an attorney for the plaintiffs in the case, said the ruling would mean cutting the prison population to around 109,000 inmates from about 119,000 currently, which amounts to about 150 percent of capacity for the prison system.
"The ruling is absolutely essential in order for prisoners to be safe and to get adequate healthcare," Specter said.
Brown said in a statement that the state would seek an immediate stay of what he termed an "unprecedented order to release almost 10,000 inmates by the end of this year."
A spokesman for the California Department of Corrections and Rehabilitation declined to provide immediate comment. (Additional reporting by Laila Kearney in San Francisco; Editing by Cynthia Johnston and Eric Walsh)