That, however, would require Republicans to approve the rest of the package knowing that the prison changes would be added.
"If we don't achieve these measured, thoughtful, I think smart-on-crime proposals, then we really are in a position where we have nothing left to do but talk about early release," Cate said.
If it passes, the prison plan would be a prime example of how the budget crisis could force California to make changes that have long been talked about, but have proven politically difficult. It would amount to a significant reversal of a decades-long pattern of longer sentences and rising prison populations.
Steinberg told reporters that the proposal would target the "revolving door" that state prisons have become for lower-level offenders.
The plan resembles recommendations from experts on reducing California's prison overcrowding, which is the focus of a federal lawsuit in which judges have been considering whether to order a mass inmate release.
"We have not done a very good job in California of distinguishing between people who are violent and who belong in prison for a long time, and those who could succeed on the outside with supervision, who have not demonstrated any history of violence," Steinberg said.
The prison plan would give state corrections officials authority to allow any inmate with 12 months or less on his or her sentence to serve the remaining time on home detention with electronic monitoring.
Inmates who are over 60 or medically incapacitated could also get home detention or be confined in a hospital.
In addition, inmates who achieve milestones in rehabilitative programs, substance abuse treatment, vocational training or education could receive up to six weeks off their prison terms.
The plan includes Schwarzenegger's proposal to release and deport illegal immigrant felons, and a scaled-down version of another proposal of his to change some felonies to misdemeanors so inmates could be held in county jails instead of prisons. Sentences for property crimes also would be scaled back.
A "Parole Re-Entry Accountability Program" would reduce the state parole population by 46,000 -- more than a third of those now under supervision -- depending on their crimes and behavior.
Those former prisoners convicted of the least serious crimes would not be subject to parole revocation that could return them to prison.
The budget plan also would create a sentencing commission to reexamine the state penal code, which would not save money immediately but would advance plans under discussion by lawmakers for years.
The commission would have three years to establish new sentencing guidelines.
Shane Goldmacher and Molly Hennessy-Fiske contributed to this report.