A registered sex offender has filed suit against four Orange County cities, challenging the constitutionality of a law that bans sex offenders from using public parks, beaches and even some roadways.

The lawsuit is aimed at Costa Mesa, Huntington Beach, Seal Beach and Lake Forest, which have all modeled local ordinances on the county's law that bans sex offenders from entering county parks, beaches and other public facilities. The suit also names Orange County Sheriff Sandra Hutchens and the four cities' police chiefs.

The ban is considered one of the most aggressive sex offender laws in California.

The lawsuit, filed in U.S. District Court on Oct. 1, claims the local laws that ban the plaintiff from entering city parks or other public facilities violate the Constitution and his protected rights under the law.

The San Francisco law firm representing the man, identified only as "John Doe" in the lawsuit, said the ban violates his 1st, 5th and 14th Amendment rights.

The lawsuit alleges that the plaintiff, by being banned from entering public property, is unable to peaceably assemble, speak freely, travel via some public roads, receive information and petition the government. The ban also deprives him of his liberties without a fair hearing and prevents him from judicial access, the lawsuit says.

Susan Kang Schroeder, chief of staff to the Orange County district attorney, defended the local laws as constitutional. Fourteen cities in Orange County have now adopted sex offender rules at the urging of the district attorney.

"Protecting children from sexual predators, I believe, is one of the most important duties of government," Schroeder said.

She said the district attorney's office will work with the cities to defend the sex offender laws.

"First of all, it doesn't surprise me that a San Francisco lawyer would be filing a suit on behalf of a sex offender," Schroeder said.

Dennis Riordan, the attorney who filed the suit, dismissed the remark.

"If that is the level of legal analysis on which these cities and county are going to be defended, they are going to be very poorly served in their representation," he said.

The lawsuit asks the courts to permanently stop the four cities from enforcing their bans and declare the laws unconstitutional.

"Last month, the state court in San Diego struck down residency prohibitions as they applied to past sex offenders, based on the constitutional right to travel within the state," Riordan said. "I don't believe anyone who reviews that opinion would doubt that we have an extremely meritorious constitutional claim in this case."

Irvine School of Law Dean Erwin Chemerinsky, a renowned constitutional scholar, said he hasn't seen the lawsuit to say whether it stands a chance in court. However, he said the county and local ordinance banning sex offenders from entering parks or beaches are weak before the law.

"I think there are serious constitutional problems with these ordinances," he said. "They are constitutionally vulnerable to challenge."

The plaintiff was convicted more than 15 years ago, the suit said, and has long since served his sentence and been treated and is now employed and married with children. However, Riordan would not provide his exact offense, out of fear it might identify him, he said.

mona.shadia@latimes.com

Twitter: @MonaShadia