SAN FRANCISCO -- A lawsuit challenging a sex offender residency restriction passed by California voters in November was dismissed by a federal judge in San Francisco Thursday.

U.S. District Judge Jeffrey White said in a brief ruling that the plaintiff, an anonymous former offender known as John Doe, had no basis for the lawsuit because the restriction doesn't apply retroactively.

The voter initiative, known as the Sexual Predator Punishment and Control Act, expanded previous restrictions and bars registered sex offenders from living within 2,000 feet of a school or park.

Lawyers for John Doe had argued the measure would prevent registered sex offenders from living in "virtually every residential neighborhood in every city in California" as well as many suburban areas.

John Doe, who pleaded guilty to a sex offense more than 20 years ago and served three months in confinement, said he feared the law would force him to move from his home, in an unidentified Bay area community. He argued that would violate a constitutional ban on laws that retroactively increase punishments for a crime.

But White wrote that since all parties in the case now agree that the law doesn't apply retroactively, John Doe has no standing to challenge the measure.

However, the judge noted there is disagreement about how the law will apply to any of the 90,000 currently registered sex offenders who move to a new residence in the future.

John Doe's lawyers say the law shouldn't apply to offenders convicted before Nov. 8, while Gov. Arnold Schwarzenegger says that those who were released before Nov. 8 are exempted.

But state Attorney General Jerry Brown contends it should apply to any registered sex offender who moves in the future.

White, implying that he disagrees with Brown, said that under either John Doe's or the governor's interpretation, John Doe would not be affected and therefore can't sue.

Brown spokesman Nathan Barankin said, "We're pleased that the challenge was thrown out as we urged the court to do, but we're still looking for a definitive ruling on the precise scope of the restriction."

Barankin said the clarification may come in a similar case pending before U.S. District Judge Lawrence Karlton in Sacramento.

Lawyers for John Doe were not immediately available for comment.