PROVIDENCE — Rhode Island’s laws on third-party ballot access are needed and constitutional, and a federal lawsuit contesting them should be dismissed, the state attorney general’s office argued in a court filing Monday.

In a brief filed with U.S. District Judge William C. Smith, Assistant Attorney General Thomas A. Palombo noted that at least two other parties in recent history — the Cool Moose Party and the Green Party — have gotten onto the statewide ballot under the provisions of the law.

The Moderate Party of Rhode Island, headed by Kenneth Block of Barrington, is challenging the ballot access laws. Currently, state law provides two ways for a new party to be listed on the ballot: if a party-picked candidate for statewide office in the prior election garnered at least 5 percent of the vote, or if it presents a petition bearing a number of signatures equal to at least 5 percent of the turnout in the prior election.

In this case, the Moderate Party would have to garner about 23,500 signatures to gain a spot on the 2010 ballot.

What the party is challenging in federal court, represented by the Rhode Island Affiliate of the American Civil Liberties Union, is the 5-percent minimum and the law’s stipulation that it cannot begin gathering signatures until Jan. 1 of the election year. The suit contends that the signature bar is set too high and that the time restriction is unconstitutional.

But Palombo argued Rhode Island has a right to set a limit to prevent frivolous parties from getting on its ballots.

“The state understandably and properly seeks to prevent the clogging of its electoral machinery, avoid voter confusion and assure that the winner is the choice of a majority, or at least a strong plurality, of those voting without the expense and burden of runoff elections,” Palombo wrote, quoting a 1968 federal ruling in another case.

He cited Georgia and Maine laws that set similar 5-percent signature standards.

Palombo was also dismissive of Block’s complaint about the Jan. 1 start date, arguing that in 2008 Senate candidate Christopher Young collected 1,000 signatures between July 1 and July 11. Extrapolating on that rate, he said allowing a new party 210 days was not “burdensome.”

The ACLU is expected to file a response to the state’s brief.

jhill@projo.com