Updated: 11:49 a.m.

Sen. Roy Blunt (Mo.) is running for Republican Conference vice chairman, setting up a head-to-head contest for the No. 5 leadership position with Sen. Ron Johnson (Wis.), who announced his candidacy weeks ago.

“After receiving encouragement from a number of my colleagues, I’ve decided to run for Senate Republican Conference vice chairman,” Blunt said. “America is facing a critical moment when we’re going to decide who we’re going to be as a nation, and I believe this is a good way for me to continue to contribute to this historic debate.”

Blunt, who serves on Sen. Jon Kyl’s (R-Ariz.) Whip team, has been quietly exploring a bid for Conference vice chairman since Sen. Lamar Alexander’s (Tenn.) decision to step down as Conference chairman caused a shake-up in the GOP leadership team. Blunt previously served as House Majority Whip and, briefly, as House Majority Leader.

Johnson, after announcing his bid for Conference vice chairman, unveiled a slate of about 10 endorsements, including from stalwart conservatives such as Sens. Jim DeMint (S.C.) and Marco Rubio (Fla.), another freshman elected in 2010. However, it is unlikely an experienced leadership hand like Blunt would run if he didn’t think he could corral votes.

Senate Republicans are set to vote Dec. 13 on a new slate of leaders.

Besides the Blunt-Johnson matchup, the leadership elections are likely to feature two easy contests, with Sen. John Thune (S.D.) expected to move up from Policy Committee chairman to Conference chairman, the No. 3 leadership position, and Sen. John Barrasso (Wyo.) expected to move up from Conference vice chairman to Policy Committee chairman.

The elections will take place during the Republicans’ weekly policy lunch and will take effect Jan. 26, when Alexander is set to relinquish his leadership post. Additional leadership elections for the 113th Congress will be held in 2012, following the presidential and Congressional elections.