It is intended to cut $1.2 billion from corrections spending as part of a state deficit-cutting deal struck last month.
Passage was less certain in the Democrat-controlled Assembly, which was scheduled to take up the measure later Thursday. For instance, three Democratic Assemblymembers are planning to run for state attorney general next year and are reluctant to vote for any bill that might make them appear soft on crime.
Republicans offered angry denouncements on the Senate floor. They said provisions to reduce some crimes to misdemeanors, release certain inmates before they have completed their sentences and ease conditions for parole would be a threat to public safety.
Sen. George Runner, a Republican from Los Angeles County, said he could guarantee a future ballot initiative to repeal the bill if it becomes law.
"This is such an over-the-top threat to public safety to the people of California, that I guarantee there will be a referendum ... because the people are not going to let this happen to them," Runner said.
Debate on the measure took on new urgency when more than 1,000 inmates rioted overnight Aug. 8 at California Institution for Men in southern California. The prison was designed to hold about half as many inmates, though investigators say they don't know if crowding helped spark the racially charged riot.
The measure passed the Senate on a 21-19 vote after a 3 1/2 hour debate. It had just enough votes to pass, with four Democrats and all Republicans opposed.
"This is an opportunity to do better and to begin to change the embarrassing fact that we spend more money on prisons than we do the University of California system," said Senate President Pro Tem Darrell Steinberg, a Democrat from Sacramento.
If also approved by the Assembly, the governor's proposal would release or divert from state prisons 27,000 inmates in the current fiscal year and another 10,000 in the fiscal year that begins next July.
It would do so through a range of measures:
- Inmates with less than 12 months to serve, who are over age 60 or who are medically incapacitated could be released from prison and given home detention with electronic monitoring.
- Sentences for certain property crimes will be lowered to misdemeanors, meaning convicts won't have to spend time in prison. Those include vehicle theft, petty theft with a prior conviction, receiving stolen property and check-kiting, a scam that primarily targets banks with fraudulent deposits.
- Allow more inmates to gain early release by completing educational, vocational or substance abuse rehabilitation programs.
- Ease supervision for thousands of parolees, making it more difficult to send them back to prison for violations.
The package also would establish a commission to review California's sentencing guidelines. Opponents fear its primary mission would be to determine whether some sentences could be lessened as a way to take pressure off an overcrowded prison system.
The new guidelines would be due by July 2012. The changes would take effect automatically unless they were rejected by the governor and a majority vote in the Legislature.
"Is this something that came out of Mad Magazine?" asked Runner, who has authored several anti-crime initiatives aimed at sex offenders and gang members.
Sen. Gloria Romero, a victim of a violent robbery in 1995, said California should join the federal government and 22 other states that have created sentencing commissions.
"There is a need to bring a smartness. Toughness alone will not bring us out of this prison crisis," said Romero, a Democrat from Los Angeles who has pushed for a sentencing commission for years. "We either do it or the judges will not only do it for us, they'll do it to us."
Schwarzenegger's office said failure of the bill would leave a $1.2 billion hole in the state's budget and force California to find other ways to release inmates. A panel of federal judges earlier this summer ordered the state to reduce its inmate population by 40,000 over two years.