By Edward Epstein, CQ Staff

Prolonged cheering and applause could be heard through closed doors Wednesday morning as Sen. Hillary Rodham Clinton went before the House Democratic Caucus to urge unity behind her victorious presidential campaign rival, Sen. Barack Obama .

“There was a great mood and she offered scintillating remarks on our need for unity,’’ said Rep. Alcee L. Hastings , D-Fla., as he left the 20-minute session in the Capitol’s big basement meeting room. He had supported the New York senator’s bid for the Democratic presidential nomination.

“It was very supportive. Sen. Clinton gave a wonderful unifying speech,’’ said Rep. Diana DeGette , D-Colo., another Clinton supporter. She said attendance was greater than normal at the House Democrats’ weekly meeting. Not only that, “people made sure they sat in the first few rows, not like in class or in regular caucus meetings,’’ she said.

“It was about unifying and addressing the issues that really matter to working families,’’ said Rep. Tim Walz , D-Minn., who endorsed Obama after the Illinois senator won Minnesota’s Democratic caucuses in early February.

Clinton, who conceded the nomination to Obama a few weeks ago, returned to her Senate duties Tuesday. She attended Democratic senators’ weekly luncheon, where her colleagues received her warmly amid calls for unity as the party gears up for what optimistic party leaders hope will bring them the White House and bigger House and Senate majorities.

In the hallway after the House caucus, Clinton spoke of the importance of this year’s election.

“This is a make-or-break election and I am 100 percent committed to make sure I do all I can to make sure Sen. Obama is sworn in as the next president of the United States,” she told reporters.

Even as she resumes her Senate duties, Clinton will make her first appearance June 27 as part of the Obama for president campaign. The two senators plan a joint campaign appearance in aptly named Unity, N.H. , where each got 108 votes in the state’s Jan. 8 primary.

First, however, Obama and Clinton will meet in Washington Thursday behind closed doors with some of Clinton’s biggest campaign donors. Obama hopes the former Clinton money people will now help his general election campaign.

In turn, Obama this week appealed to some of his own big donors to help Clinton pay off the $10.35 million in primary campaign debt she faces. That doesn’t include another $11 million that she lent her campaign.

Speaker Nancy Pelosi , who until Obama won enough delegates to claim the nomination had remained neutral in the race, paid tribute to Clinton.

“Sen. Clinton has emerged from this election as the most respected political figure in America for now, and for a long a time,’’ the California Democrat said.