SAN FRANCISCO — California Attorney General Bill Lockyer moved late Wednesday to dismiss a federal lawsuit that challenges a voter-approved measure prohibiting registered sex offenders from living within 2,000 feet of a school or park.

Lockyer urged the lawsuit’s dismissal because the measure does not have any sanction against those who violate the 2,000-foot rule. Proposition 83 “does not call for punishment, much less imprisonment, for violation of the residency restriction,” the attorney general’s brief said.

A lawsuit challenging one of several provisions of Proposition 83 was brought by an unidentified California registered sex offender who already lives within 2,000 feet of a school or park. The plaintiff, identified in court papers as John Doe, is not on parole or probation for a sex crime. He was convicted 15 years ago and served no time.

Lockyer’s office also said the lawsuit should be dismissed because the measure does not apply to registered sex offenders like John Doe who are already living in a prohibited area and who are not on parole or probation. It was not immediately known how many California registered sex offenders are living within 2,000-foot zones and who are no longer on parole or probation.