In an unusual year with two U.S. Senate seats up for grabs in Mississippi, Republican Thad Cochran should be able to run a low-budget, low-stress campaign for re-election.

But the other race is set to become an expensive and hard-fought contest.

Three high-profile candidates qualified to run Friday for Mississippi’s U.S. Senate seat that is being filled by a special election. Republican Roger Wicker wants to retain the seat he got by appointment on Dec. 31 after the resignation of the GOP’s Trent Lott. The two Democrats who signed up to run are former Gov. Ronnie Musgrove and former U.S. Rep. Ronnie Shows.

Cochran, first elected to the Senate in 1978, is unopposed for his party’s nomination in his race. The two Democrats who signed up for their party’s Senate primary — former state Rep. Erik Fleming of Clinton and perennial candidate Shawn O’Hara — have lost statewide elections after failing to raise enough cash to run effective campaigns.

Friday was candidates’ qualifying deadline for the Senate seats and for four Mississippi U.S. House seats. Party primaries are March 11 and the general election is Nov. 4.

Fleming challenged Lott in the 2006 U.S. Senate campaign. Lott easily won re-election, then served one year of his six-year term before retiring last month.

O’Hara has run for a long list of offices over the past 17 years, from governor to U.S. representative. He lost a race for state treasurer last year — after initially being blocked in his efforts to qualify for several offices at once.

Cochran, 70, was chairman of the powerful Appropriations Committee when Republicans held the majority. Since Democrats took over the majority a year ago, Cochran has been his party’s ranking member on Appropriations — still a position that allows him to steer money to his home state.

Two of Mississippi’s U.S. House seats are wide open.

Republican Chip Pickering announced several months ago that he would not seek re-election in the 3rd District, which stretches from Natchez to the Jackson suburbs to Starkville. Pickering was first elected in 1996.

Wicker recently stepped down from the congressional post in north Mississippi’s 1st District because Gov. Haley Barbour appointed him to temporarily fill the Senate seat that Lott left. Wicker was first elected to the House in 1994.

The winner of the special Senate election for the seat Wicker now holds will serve until January 2013. Barbour set the special election for Nov. 4, but Attorney General Jim Hood, a Democrat, has filed a lawsuit seeking to have the election sooner. A court hearing will be held Monday in that dispute.

Friday was the candidates’ qualifying deadline for the special Senate election, according to Barbour’s order that set the election.

Barbour has not yet set a special election to fill the final months of Wicker’s House term in the 1st District. However, the special election and the primary are expected to be close together — creating extra work for candidates and confusion for voters.