While much of Washington is focused on a potential battle for Senate Majority Leader between Whip Dick Durbin (Ill.) and Conference Vice Chairman Charles Schumer (N.Y.), a series of lower-profile leadership races are also percolating just below the surface among a handful of ambitious junior Senators.

If Majority Leader Harry Reid (D-Nev.) were to lose his re-election bid this fall, Durbin and Schumer are all but certain to duke it out to succeed him. And that likely contest would open up the No. 2 spot regardless of who prevailed since, knowledgeable Democrats say, neither Durbin nor Schumer would want to serve as the other’s Whip.

Conference Secretary Patty Murray (D-Wash.) would be a natural to move up in the ranks, but sources said she is unlikely to escape a challenge for Whip. Top among the possible contenders: Democratic Senatorial Campaign Committee Chairman Bob Menendez (N.J.), the ambitious junior Senator who jumped into leadership after just three years in the chamber.

Menendez is no stranger to leadership: He served for three years as the House Democratic Caucus chairman before he was appointed to the Senate in 2006.

But climbing the Senate leadership rungs may not be so simple. Menendez is serving as DSCC chairman in a challenging election year, and while many Senators are likely to forgive him the loss of a few seats given the anti-incumbent political environment, some fault Menendez for not intervening sooner in the failed special election campaign of Massachusetts Democrat Martha Coakley against now-Sen. Scott Brown (R). Menendez also has had a tough time recruiting top-tier candidates and dissuading damaging primary contenders, such as Arkansas Lt. Gov. Bill Halter’s race against Sen. Blanche Lincoln (D).

The lower-key Murray, conversely, is hardly the pit bull Members generally like to see in a Whip, but one Democratic aide described her as “quietly ambitious.” And for some, she has become a go-to leader — particularly centrists and female Members — seeking help on one issue or another and is widely seen as the voice of reason in the current four-Member leadership team when discussions get off-track or heated, several sources have said.

Steering and Outreach Committee Chairwoman Debbie Stabenow (D-Mich.) is widely presumed to have her sights on a higher post, making her another possible Whip candidate. However, several sources said Stabenow is more likely to vie for the Democratic Policy Committee chairmanship being vacated by retiring Sen. Byron Dorgan (N.D.).

But Stabenow has some company: Sen. Sheldon Whitehouse (R.I.) is most often mentioned as a candidate for the DPC chairmanship, along with Sen. Amy Klobuchar (Minn.). Both Stabenow and Whitehouse would make good fits for the DPC job, one senior source said, because they have both been active recently in reconfiguring the DPC’s operations into an organization that melds both policy and public relations.

The caucus, however, does not vote on that position as it does for Leader, Whip, vice chairman and secretary; the DPC and DSCC chairmen are chosen by the Leader. The policy panel is charged with providing Senators with analyses of upcoming legislation and also hosts weekly lunches with speakers on a wide variety of policy and political topics.

Whitehouse could also be a potential candidate for Conference secretary if Murray moves up or opts not to run for it again.

Another possible fresh face for the Democratic leadership is Sen. Tom Carper (Del.), who has quietly become more helpful to Democratic leaders, such as when he inserted himself into negotiations on health care reform last year to try to break an intraparty impasse over the public insurance option. Carper, who already serves as one of three Deputy Whips, also appears to harbor ambitions for leadership, but sources said he has not appeared on many short lists for the top jobs.

Democrats said their caucus is densely populated with motivated and upwardly mobile Members. However, a third of the Members are in their first term and still learning how to be Senators, much less Senate leaders.

“The bench is very deep. It’s just also very young,” one source said. The source added of the DPC position in particular, “It’s a pretty big job for someone who’s been a Member for the blink of an eye.”

Regardless of what happens in Reid’s troubled re-election race and any subsequent leadership shuffle, the Majority Leader will have to pick new chairmen for the DPC and DSCC in November or December. Menendez is unlikely to follow Schumer’s model of serving two stints atop the DSCC since he is up for re-election himself in 2012, typically a disqualifier.

The contenders for Whip or any of the other lower-tier leadership positions could also be strongly influenced by who the leader is heading into the 112th Congress. When Reid ran for the top caucus job in 2004, he asked Durbin to run as his Whip, sources said.

Another possible question mark is whether Schumer’s position as vice chairman will continue to exist. Reid created the leadership slot for Schumer after his first run at the DSCC delivered the majority — and Reid’s title of Majority Leader — to Democrats in 2006.

“It’s unclear what would happen to the vice chair” position, another Democratic aide said. “The job was created for a very specific reason.”

And underneath it all is the question of who in the rank and file will be left standing when the dust of the election settles on Nov. 3 and whether the caucus tilts to the left or the center.

As part of that, questions will undoubtedly arise over next year’s committee leadership and which Members make a play for a plum committee assignment.

Along with Whitehouse and Klobuchar, Democratic Sens. Mark Warner (Va.), Mark Begich (Alaska), Jeanne Shaheen (N.H.) and Mark Udall (Colo.) appear to be positioning themselves for potential leadership slots in the future, but sources said it is unclear if or when any of them might try to make a move given their relative inexperience in the chamber.

Warner, however, is most often mentioned as the likely successor to Menendez at the DSCC. Klobuchar has been considered in the past for the campaign post, but she is up in 2012 would likely postpone taking on a tour at the campaign arm.

Most of the “Old Bull” Democrats already are settled in comfortable chairmanships or are retiring this year, and sources said they are highly unlikely to try to make the jump to leadership at this stage in their Senate careers.

Another source said many of the hungrier caucus Members tilt too far to the left and may not be a good fit for the myriad Democratic centrists.

“We’ve got a lot of aggressive people, but no one who could bridge the gap,” one senior Democratic source said. “Some of them are the gap.”

Though centrists such as Sens. Mark Pryor (D-Ark.) and Claire McCaskill (D-Mo.) are mentioned as rising stars with the gravitas and smarts to ascend into leadership, sources said both of them, along with other centrists, are largely precluded from playing official leadership roles because they represent swing states. Instead, both are likely to serve as leadership advisers on specific projects.

One potential dark horse candidate for leadership is Sen. Jack Reed (D-R.I.), but it is difficult to tell whether he would even want such a role. If he did, however, sources said he would be a natural fit, given his credibility within the caucus on national security issues and his longevity in the chamber.