ST. PAUL — Minnesota cities concerned about the possible release of sex offenders are passing restrictions on where they can live.

The state’s ongoing legal fight with the federal judge who ruled its sex offender program unconstitutional last year has sparked concern about offenders moving into communities. From tiny Minnesota Lake to Brooklyn Center, the number of ordinances restricting sex offender residency has more than doubled to 39 in the past year.

But those policies aren’t without their own concerns, as some worry they’re vulnerable to legal challenge. A group of Minnesota legislators is pushing a bill that allows cities and counties to pass tougher ordinances that keep Level 3 offenders — the most likely to re-offend — away from schools and parks, seeking to give local governments a stronger case to defend if a lawsuit comes.

“What they’re worried about is that eventually someone will challenge it,” said Rep. Jim Newberger, the Becker Republican behind the bill. “There’s no statute to back it up right now.”

U.S. District Judge Donovan Frank ruled Minnesota’s program unconstitutional in June, citing the rarity of releases of the more than 700 inmates. Just a handful of inmates have been conditionally released in its 20-year history.

But even as state officials insist the program is constitutional, Gov. Mark Dayton is taking steps to comply with Frank’s order. He is proposing funding for less-severe treatment centers and a series of new evaluations that could eventually lead to more offenders being released.

After imposing a temporary ban on sex offender relocation last fall, Brooklyn Center’s city council passed residency restrictions late last month that set 2,000-foot boundaries around schools, playgrounds and child care centers. The Minneapolis suburb’s mayor said he supports Newberger’s bill.

“If the legislation passes, now we’ve got something we can point to and say, ‘the state specifically says we can do that,”’ said Mayor Tim Willson.

But Department of Corrections Commissioner Tom Roy said he worries that a string of court decisions in other states that have struck down residency restrictions could mean trouble for Minnesota. He said he’s concerned about the rise in city restrictions because he thinks they don’t hinder offenders from committing more crimes.