A federal judge ruled Friday that California's ban on sex offenders living within 2,000 feet of places where children gather can't be applied retroactively.

U.S. District Judge Lawrence Karlton said there was nothing in the so-called Jessica's Law that specified its provisions were intended to be applied retroactively. He added that state law requires the statute apply from the date it takes effect.

More than 70 percent of voters approved the measure, Proposition 83, on Nov. 7 and it took effect the next day.

The law prohibits registered sex offenders from living within 2,000 feet of a school or park, effectively banning paroled sex offenders from many California communities. It also requires lifetime satellite tracking for some paroled sex criminals upon their release from prison.

Supporters said the initiative would save lives, but law enforcement and social workers worried that some sex offenders may simply stop reporting their addresses so they will not have to move. There are about 90,000 registered sex offenders in California.

The case is one of two lawsuits that asked federal judges to interpret the restrictions.

A day after the election, a federal judge in San Francisco temporarily blocked the 2,000-foot residency requirement from applying to current registered sex offenders who are not on parole or probation.

Karlton's decision Friday came in response to a lawsuit filed by three unidentified sex offenders, including one on parole and one on probation, who said they lived within 2,000 feet of schools or parks.

The attorney for the three plaintiffs, Scott Wippert, said he interpreted the decision as also freeing sex offenders who were released before the measure was passed from its provisions requiring lifetime satellite tracking for felony sex offenders.

Department of Corrections and Rehabilitation spokesman Bill Sessa said the ruling wouldn't affect residency and monitoring requirements the state imposed on paroled sex offenders before Proposition 83 was approved.

Those laws require parolees to live more than 2,000 feet from where children congregate for three years after they're released, Sessa said.

"Sex offenders, out of all our parolees, are on the shortest leash and under the biggest microscope of any of them," Sessa said.

Gareth Lacy, spokesman for Attorney General Jerry Brown, said his office was still interpreting the judge's order. He said Brown's goal is to implement the law in a way that protects Californians and gives guidance to law enforcement.

The proposition is named for Jessica Lunsford, a 9-year-old Florida girl who was kidnapped, raped and killed last year. John E. Couey, a convicted sex offender who had been living within sight of Jessica's home, is expected to stand trial in her death this month.