The anticipated departure of Rep. Rahm Emanuel (D-Ill.) to become President-elect Obama’s chief of staff has set off a surprise post-election scramble in House Democratic leadership ranks.

With Emanuel all but certain to quit his fourth-ranking post as chairman of the Democratic Caucus for the White House job, the field of possible successors was taking shape Wednesday, even as the dust settled from Democratic victories on Tuesday.

And that wasn’t the only possible Democratic shake-up on a day the party expected to celebrate a gain of about 20 seats. Oversight and Government Reform Chairman Henry Waxman (Calif.) planned to challenge Energy and Commerce Chairman John Dingell (Mich.) for the top slot of that committee in a fight of two old bulls.

So far, the race for Caucus chairman is a two-way matchup pitting Vice Chairman John Larson (Conn.) against Rep. Chris Van Hollen (Md.), who engineered the 20-seat gain as chairman of the Democratic Congressional Campaign Committee.

Van Hollen had a standing offer from Speaker Nancy Pelosi (D-Calif.) to do a second tour heading up the party’s campaign arm, but he made clear on Wednesday that he wasn’t interested.

“I’m exploring all my options,” Van Hollen said at a midday press conference. “One option I’m not exploring is continuing as chairman of the DCCC.”

Instead, a senior Democratic aide said, Van Hollen is eyeing a run to replace Emanuel, whom he followed at the DCCC. He will have to defeat Larson, who briefly chaired the Caucus when Democrats were in the minority. Larson essentially handed the post to Emanuel at Pelosi’s urging as a reward for quarterbacking their comeback when Democrats retook the House.

Van Hollen and Larson have begun calling colleagues to lock up support. But the race is just beginning, and others could jump in. Also being watched Wednesday was Rep. Xavier Becerra (D-Calif.), already in leadership as assistant to the Speaker, an appointed role.

Becerra, a past chairman of the Congressional Hispanic Caucus, could point to the emerging importance of Latino votes in the Democratic coalition as an argument for promoting him over two white competitors. “Diversity is a premium,” one Democratic strategist said. But it is not yet clear whether he would be willing to give up a guaranteed seat at the leadership table to chance a run for an elected position. Becerra’s spokeswoman declined to comment, and several Democratic sources said the lawmaker has been coy about his plans.

If Becerra makes the race, it would open up his appointed slot. The profile of the new leadership lineup would likely guide Pelosi’s decision about how to fill that position in a way that balances the team, aides said.

Larson’s move into the race for Caucus chairman means he is giving up his position as vice chairman, opening that slot for a new generation of leadership hopefuls. Two young Florida Members — Reps. Debbie Wasserman Schultz and Kendrick Meek — would be top contenders, if they make the race — as would Rep. Joe Crowley (N.Y.), whom Larson defeated in a 2005 vice chairmanship contest.

All three Democrats are on the short list to replace Van Hollen at the DCCC. But an elected leadership post offers a step up the ladder, while the campaign committee job comes with the headache of a grueling travel schedule in a cycle when Democrats are expected to be on defense. “Normally, people do DCCC chair to get in position to run for leadership,” one strategist said. On the other hand, “the way Caucus politics work, you get in the ladder and keep climbing. It’s getting in that’s the hard part.”

Further complicating the picture and potential contenders’ thinking about it was a persistent rumor of another imminent vacancy, opened by Majority Whip James Clyburn (D-S.C.) moving to head up the Department of Housing and Urban Development or the Department of Transportation. Clyburn aides dismissed the talk of any such move.

Amid the jockeying, House Democrats were pondering the prospect of losing one of their strongest strategists to the Obama White House. “It’s good for the House to have one of our own as the president’s right-hand man,” one Democratic leadership aide said. “At the same time, it’s a terrible brain drain to the leadership team.”

Few Members can boast such a varied résumé: Emanuel has served in the Clinton White House, worked in investment banking and proved to be an astute political and legislative tactician.

Sources who worked with Emanuel when he was a senior aide to former President Bill Clinton describe him as surprisingly less partisan than might be expected of someone who, as DCCC chairman, led Democrats back into the majority in 2006.

“He was the guy in the Clinton White House who was most motivated by getting things done,” said Joel Johnson, who as a senior strategist for former Senate Majority Leader Tom Daschle (D-S.D.) worked regularly with Emanuel.

“For those of us who knew him in that period, he was not a partisan player — he was a very practical political strategist with a real track record of success,” said Johnson, who went to work for Clinton after Emanuel left.

Those who worked at the White House with Emanuel said he is prepared to be chief of staff as a result of his varied duties under Clinton that included running legislation such as the North American Free Trade Agreement and the program to put police officers on the streets, devising daily and long-term communications strategies and dealing with Capitol Hill.

His drive will help keep the White House on track amid distractions and competing influences, one former Clinton staffer said.

“Rahm would be good at making sure Obama and his agenda are foremost on the minds of the Hill,” this official said. “Things like the Congressional schedule and the budget process can pound on you and you can become reactive.”

Another source who worked with Emanuel at the White House said he suspects part of the reason Emanuel will take the job is the chance to act on what he learned during Clinton’s rocky tenure about how not to run the place.

“He probably has a very good feel for what was done right and what was done wrong,” he said. This source described Emanuel as a tough and effective manager but warned prospective Obama staffers that they will be expected to perform.

“He’s incredibly smart and quick and a great person to work around, but if you screw up, you will hear about it,” he said.