Voter-approved limits on where sex offenders can live may be enforced on parolees who committed their sex crimes long before Jessica's Law passed, the California Supreme Court ruled Monday.

But the court did not clarify what happens once they leave parole, or if the law applies to county probationers, frustrating law enforcement officials who had hoped the court would settle vexing questions over the most controversial provision of a 2006 ballot measure backed by 70 percent of voters.

The ruling means state parole agents can continue their strict enforcement of a ban on sex offenders living within 2,000 feet of a school or park where kids "regularly gather."

"It matters not ... whether the registered sex offender is being released on his current parole for a sex or nonsex offense," Justice Marvin Baxter wrote in the majority opinion. To rule otherwise, he wrote, would grant parolees with earlier sex convictions "a free lifetime pass" from the ban.

Justices Carlos Moreno and Joyce Kennard dissented, arguing that the ban should apply only to those convicted of sex offenses after the law passed.

Critics say the 2,000-foot rule has forced thousands of parolee sex offenders into homelessness and raised the risk of reoffense. Since the law passed, the number of paroled sex offenders who register as transients has risen from less than 100 to more than 2,200. The ranks of homeless sex offenders increased dramatically over the past year, after state parole officials cut back on paying for motel rooms and apartment rents for many sex offenders.

"There definitely are challenges in certain areas to find locations in big cities, well-populated areas. I think we've handled those very well as a department," said Gordon Hinkle, spokesman for the state Department of Corrections and Rehabilitation. "We're pretty pleased with the ruling."

The plaintiffs in the case are four registered sex offenders who committed their sex offenses before the law passed - in some cases decades earlier - and were released from prison after serving time for other crimes. They claimed the ban amounted to retroactive punishment, which the court rejected, 5-2.

They also argued that the law is unconstitutionally vague and that the 2,000-foot rule infringes on various constitutional rights, including property and privacy rights, by severely limiting where they can live. The court left that question open, however, saying the plaintiffs would need to show evidence to lower courts that the law virtually shuts them out of housing.

The ruling sets up potentially hundreds or thousands of lower court challenges by individual sex offenders. Some law enforcement experts predicted lower courts may find the 2,000-foot rule unconstitutional in counties like San Francisco, where there is scant housing outside the zones, but legal elsewhere.

"This case is not over," said Jake Goldenflame, a convicted sex offender and advocate. "It is just beginning."

Gov. Arnold Schwarzenegger praised the decision in a statement Monday.

"The voters passed this important initiative to help protect our communities and our children from sexual predators and I am pleased the court ruled today to uphold the will of the people," he said. "My Administration will continue to do everything within our power to protect California's children and families from the threat of sexual predators including defending Jessica's law."

Ernest Galvan, an attorney for the plaintiffs, said the ruling, and the constitutional questions it left open, warrant a change in the law.

"This is in no way a green light for rousting sex offense registrants out of their homes or starting a round of local enforcement of these residency restrictions," Galvan said. "There are still very grave constitutional doubts about this law. The best thing to do would be for the Legislature to fix it."

Proposition 83, backed by 70 percent of voters in 2006, stiffened penalties for some sex crimes, required lifetime GPS monitoring of newly released sex criminals and set the 2,000-foot "predator free zones." It is considered among the nation's stiffest anti-predator laws.

About 90,000 registered sex offenders live in California, including about 23,000 now in prison. About 10,000 are either on parole or probation.

"I don't think we can count on the courts to answer all of these things, when experts statewide are saying this is a broken process," said Robert Coombs of the California Coalition Against Sexual Assault, a victim advocacy group.

"You're now 3.5 years into a law that everybody said, 'We'll look to the courts to figure this out.' And for 3.5 years sex offenders are going homeless. It's time for the policymakers to roll up their sleeves."