Ohio Democrats appear set to host a contentious primary to decide their nominee for the open Senate race in 2010 — in what amounts to the first intraparty battle to emerge this cycle.

Lt. Gov. Lee Fisher (D) and Ohio Secretary of State Jennifer Brunner (D) are announcing their campaigns Tuesday, setting up what is likely to be a bruising battle between two statewide office holders unless national or state party leaders intervene.

In a video on her campaign Web site, Brunner stated her intention to run for the seat held by retiring Sen. George Voinovich (R-Ohio).

“I’m running for the United States Senate to be part of the solution, to meet our challenges and to help Ohio emerge stronger than ever,” Brunner says in the video.

Fisher announced last week that he was forming an exploratory committee to look at running. According to a Fisher spokeswoman, the Democrat will announce his candidacy 6 p.m. Tuesday with Gov. Ted Strickland (D) at his side.

While Strickland has clearly signaled he will support Fisher in the primary, it would not be unprecedented for national party leaders to wade into the contest as well if one of the two candidates is viewed as the stronger general election nominee.

In 2006, the Democratic Senatorial Campaign Committee — then headed by Sen. Charles Schumer (N.Y.) — caught flak from some liberal party activists for getting involved in clearing the primary fields in Ohio and Pennsylvania. In both cases the Democratic nominees were victorious in November after avoiding bloody primary fights.

Ohio Rep. Tim Ryan (D) and Zack Space (D) are also mentioned as possible Senate candidates, but neither lawmaker has made any moves that would indicate they are preparing to run for the seat.

Republicans, meanwhile, are less likely to have a multicandidate competitive primary contest. Buckeye Republicans and national party officials have lined up behind former Rep. Rob Portman (R-Ohio), although state Auditor Mary Taylor (R) is still strongly considering a bid.