CINCINNATI (AP) - Two third-party presidential candidates filed a federal lawsuit Monday to force a recount of Ohio ballots, and a spokesman for the state Democratic Party said it intends to join the suit.

The lawsuit was filed Monday evening in U.S. District Court in Toledo, according to Blair Bobier, a spokesman for Green Party candidate David Cobb, who brought the suit along with Libertarian Michael Badnarik. Court officials could not be reached for comment Monday night. The case did not immediately show up on the court's Web site.

The third-party candidates have said they are not interested in overturning President Bush's victory in the state. But they say they are concerned about reports of voting irregularities and believe a recount is necessary to ensure accuracy.

Dan Trevas, spokesman for the Ohio Democratic Party, said the party would join the recount request after the secretary of state certified the results, or sooner if an early recount is ordered by a court.

Carlo LoParo, spokesman for Secretary of State Kenneth Blackwell, has said results will be certified by Dec. 6, and said Monday it would not be feasible to conduct a recount beforehand because there are no final numbers.

Bush led Democrat John Kerry by 136,000 votes in the unofficial count, and Kerry conceded that there were not enough provisional ballots to change the outcome. But Kerry supporters have made numerous claims of voting irregularities in Ohio.

The two third-party candidates received a combined 0.26 percent of the vote in unofficial results.

Keith Cunningham, director of the Allen County Board of Elections and incoming president of the Ohio Association of Election Officials, called the lawsuit "frivolous," adding that he might mobilize counties to resist a recount.

"Commissioners are beginning to understand - and if they don't, will understand soon - what kind of financial impact this is going to have on them, in a year when elections already cost a great deal more than expected," said Cunningham, a Republican.

The two former third-party candidates have said they raised more than $150,000 to cover the state's fee for a recount. Ohio law requires payment of $10 per precinct, or $113,600 statewide, but election officials say the true expense would be far greater.

LoParo has estimated the actual cost at $1.5 million.