Correction Appended

Even as Sen. Barack Obama (Ill.) claimed the Democratic nomination for president Tuesday night, Senate Democrats treaded carefully over the news to avoid alienating his unsuccessful rival and their soon-to-be-returning colleague, Sen. Hillary Rodham Clinton (N.Y.).

Most Senate Democrats, both committed and uncommitted, said Tuesday that they would wait until the final votes in Montana and South Dakota had been cast — and Clinton had absorbed the news — before rallying behind the inevitable Obama candidacy. However, other superdelegates, including many House Democrats and prominent party officials, began a charge toward Obama’s camp earlier in the day that lasted into Wednesday night after Obama took the delegate edge.

Senate Majority Leader Harry Reid (D-Nev.), who has been steadfastly neutral in the race, tried to set the tone for what’s been at times an awkward and divisive competition between two rising stars in his party’s Conference. Reid said Tuesday that he would endorse later in the week — presumably Obama — and urged other Democrats to follow suit, but at the same time, he told Senators to keep their powder dry until the final primary outcomes were known. Reid and House Speaker Nancy Pelosi (D-Calif.) asked delegates on Wednesday morning to make their picks public by Friday.

“I want everyone to wait until the elections are over,” Reid said.

Reid said Clinton “needs to be left alone” to determine her next move, and after that is clear, he “will set an example for the rest of the Senate, as I always try to do as the leader.” Reid said he would endorse no later than Friday and predicted “most of this will be done by the end of the week.”

To that end, Reid wrote a letter with Pelosi and Democratic National Committee Chairman Howard Dean on Wednesday urging the remaining undeclared superdelegates to commit to a candidate. That letter called for party unity in the wake of the months-long campaign, while simultaneously congratulating both candidates for waging an engaging and spirited campaign that brought out millions of new Democratic voters.

Party leaders have tried to retain their impartiality throughout the race and aim to handle Clinton’s exit with similar restraint. The stakes are greater in the Senate because Clinton is expected to return to her duties at some point, but all Democrats know — now more than ever — that her loyal voters are critical to a White House victory in November.

“We need Hillary Clinton’s support in the general election. We need to make sure we are gracious to her,” said a senior House Democratic aide. “It’s the right thing to do. She’s run a great race. She’s attracted a record number of voters. We want to make sure everyone is working together. The only way to win is if we are unified.”

Senate Democrats widely embraced that sentiment Tuesday, saying that there’s widespread belief that she deserves their respect as she decides how to end her campaign. With the exception of the Montana Democrats, Sens. Max Baucus and Jon Tester, the majority of the outstanding uncommitted Senate superdelegates seemed inclined to wait to endorse Obama until Wednesday at the earliest.

“We need to wait to give Sen. Clinton room to make the decision that many think she is going to make,” said Sen. Ken Salazar (D-Colo.), one of the few remaining uncommitted Senators. “I just think that people should relax.”

Salazar was one of four unpledged Democratic Senators who met privately Monday afternoon to discuss superdelegate endorsements and efforts to try to unify the party in the wake of the primaries. No conclusions were reached, but the quartet seemed to agree that they needed to — and would — weigh in before the week was out.

Although not a participant at Monday’s session, another uncommitted Senate Democrat, Sen. Sherrod Brown (Ohio), said he would heed that call, although he also said he felt it was appropriate for his colleagues to wait until the final votes are counted in Montana and South Dakota. He said he would endorse by Friday.

“We all want it done this week,” Brown said, deflecting questions about why he chose to wait until now and what it means in terms of his support. “You can read into that what you want.”

The cautiousness from Democratic Senators contrasted with the House, where the roughly 50 Democratic Members yet to endorse in that chamber began a trickle to Obama that is expected to become a flood in coming days.

Most notable among them was House Majority Whip James Clyburn (S.C.), the chamber’s highest ranking black Member, who announced his long-expected endorsement of Obama on NBC’s “Today.”

“He is elevating the political rhetoric. He is elevating our party. He is energizing our party. He is bringing to the process new voters,” Clyburn said.

Later in the day, he predicted Obama would wrap up enough support to claim the nomination as early as Tuesday night. In addition to Clyburn, Obama also claimed the backing of Reps. John Spratt (S.C.), Carolyn Cheeks Kilpatrick (Mich.), John Olver (Mass.) and Maxine Waters (Calif.).

One Democratic aide close to the Obama campaign said their superdelegate strategy all along was based on not having to involve Democratic leaders in forcing the contest to an end. Rather, Obama’s camp wanted rank-and-file lawmakers and other party officials across the country to help him reach the nomination threshold.

“I think it’s more helpful to have Members bring him over the top than to have leadership be the ones to step in and do it,” the Obama aide said. “So in the end, it worked out for the best.”

Last week, surrogates for the Obama campaign were contacting uncommitted Members and asking whether they would be willing to come out and make their support public on Monday or Tuesday before primary voting concluded, or if they would they be willing to have their support made public Tuesday evening after polls close in Montana and South Dakota. The exact length of the list of supporters the campaign planned to make public remained unclear as of Tuesday afternoon.

“There will be a list of names released after the polls close,” the aide said.

Sen. Bill Nelson (Fla.), who endorsed Clinton early on, conceded that if Obama is able to match and exceed by a healthy margin the number of delegates needed to clinch the nomination, the dynamics of the race will change. While unwilling to predict that result just yet, Nelson said Democrats will unify around one candidate within the coming days.

“Everyone will come together,” Nelson said. “We’re all human beings, and it may take a while, but for folks like me, it’s not going to be a problem.”

Sen. Ben Nelson (Neb.), who endorsed Obama earlier this year, agreed, saying: “I think the party is less disjointed than people are suggesting. There are some hard feelings that have to be dealt with, but the focus is going to quickly shift to John McCain.”

Lauren W. Whittington, Tory Newmyer and Tim Taylor contributed to this report.

Correction: June 4, 2008

The article misspelled the last name of Rep. John Olver (D-Mass.).