Ambition, leadership term limits and a pending retirement guarantee that Senate Republicans will elect a new slate of leaders in two years, as the four most-senior positions in the GOP Conference come open.

Already, two current members of the Republican leadership are soliciting their colleagues’ support in the race to succeed Majority Leader Bill Frist (R-Tenn.), who has said he will retire at the conclusion of the 109th Congress.

The race between Majority Whip Mitch McConnell (Ky.) and Republican Conference Chairman Rick Santorum (Pa.) has made it likely that the positions of Whip, Conference chairman and Conference vice chairman will go vacant, thus ensuring that at least a few new faces will take seats at the GOP leadership table.

“Senator Frist leaving and term limits will have a ripple effect,” Sen. Lindsey Graham (S.C.) said of the reshuffling of the leadership team at the end of the next Congress.

Unlike the race to succeed Frist, no clear signs of organized campaigns have yet emerged among potential candidates for these positions. But privately, Republicans are beginning to speculate about who will help lead the Conference into the 2008 presidential election.

“I think for most Members, it is still kind of amazing that this has broken out,” said a veteran Republican aide of the race to replace Frist. “The inevitable conversation about dominoes is already occurring.”

Republican Conference term limits require Santorum to step down as chairman at the end of the 109th Congress, forcing him to re-evaluate his future leadership options. McConnell, who took over as Whip in 2002, could serve two more years in that position, but allies said he views this opportunity as a chance to climb up the last rung of the leadership ladder.

Should McConnell or Santorum wrap up the leadership election in the next year, it is widely believed that the other person would shift his focus to the Whip’s race.

The race for Whip could be a crowded field. Sen. Judd Gregg (N.H.) and Republican Policy Committee Chairman Jon Kyl (Ariz.) have been mentioned as possible contenders for the Whip job, as has Sen. Bob Bennett (Utah), the current Chief Deputy Majority Whip. But Bennett said last week he is not interested in the position.

“I am more of a policy Senator than a process Senator,” he said.

The dominoes of Conference chairman and Conference vice chairman are expected to fall in tandem. Sen. Kay Bailey Hutchison (Texas) is the current vice chairwoman, but her term expires at the end of the 109th Congress. Hutchison would be a natural choice to succeed Santorum as chairman, but she is rumored to be eyeing a run for governor back in Texas.

As a result, no fewer than 11 Senators have been mentioned as possible candidates for one of the Conference slots — and this list is expected to grow and contract several times over the next two years.

Sens. Elizabeth Dole (N.C.), Lamar Alexander (Tenn.), Saxby Chambliss (Ga.), Norm Coleman (Minn.), Susan Collins (Maine), John Ensign (Nev.), Graham, Kyl, Jeff Sessions (Ala.), Gordon Smith (Ore.) and Jim Talent (Mo.) are most often cited by their colleagues as possible successors to Santorum and Hutchison.

Collins and Smith are considered centrists, while the other Senators are more closely aligned with conservative wing of the Conference. Collins acknowledged that some of her colleagues have “approached her,” but as of now the Maine Republican said she is not interested.

“I have a lot of responsibilities as chair of Governmental Affairs and I am very happy to play a leadership role through being a committee chairman,” Collins said.

A Smith spokesman said his boss is not closing the door on joining the leadership. “He is currently focused on issues of importance to Oregonians, but he is keeping his options open,” said spokesman Chris Matthews.

The dominos are unlikely to stop at the Conference chairman and vice chairman: If Kyl decides to seek a more senior role, the chain reaction could continue to the Policy Committee. At that time, Republicans will also pick a chairman to head the National Republican Senatorial Committee as well as a chairman for the Steering Committee, which is currently headed by Sessions.