Sen. John Thune (R-S.D.) plans to run for chairman of the Republican Policy Committee, a senior GOP aide confirmed Wednesday.

Thune currently serves as Conference vice chairman and would move up the ranks to fill the slot being vacated by embattled Sen. John Ensign (R-Nev.), who resigned after admitting to an extramarital affair with a former campaign staffer.

“The reality is Thune is the natural next in that position because he’s in the position that’s right below it,— the aide said. “I think he’s widely regarded as an articulate member of the caucus.—

Thune’s all-but-certain candidacy leaves his vice chairman position up for grabs. While Sen. Richard Burr’s (R-N.C.) name has been floated as a possible contender, he said Wednesday he does not intend to run. Other possibilities include Sens. Lisa Murkowski (Alaska) and Johnny Isakson (Ga.), both of whom are viewed as rising stars but like Burr and Thune are up for re-election in 2010 and may not want to entertain a leadership race.

“Like I told people back in North Carolina when I came to Washington, I want to serve my state. I don’t want to get into leadership,— Burr said.

Earlier Wednesday, Sen. Orrin Hatch (R-Utah) almost immediately reversed on a decision to run for the Republican Policy Committee chairmanship, calling it a “fleeting thought.—

The Utah Republican, who sits on the Finance; Health, Education, Labor and Pensions; and Judiciary committees, said that he has “too much on my plate.— Hatch said he would instead stand behind Thune for the No. 4 leadership job.