WASHINGTON - Barack Obama told Hillary Rodham Clinton's top financial backers Thursday that he personally has donated $2,300 to her campaign and more significantly has asked his biggest donors to help pay off her more than $20 million debt.

Obama made the announcement at a meeting with Clinton donors who have been frustrated that the Democratic presidential nominee-in-waiting had not done more to help her pay the bills even as they are expected to help fund his campaign.

The size of Obama's donation is the most he can contribute under federal law.

He received a standing ovation from the crowd of more than 200 when he said he would enlist his supporters to help pay off her debt, said Tom McMillen, a retired NBA player and former Democratic congressman from Maryland who attended. The meeting was closed to the media.

"It was really about unifying the party,'' McMillen said.

Clinton adviser Terry McAuliffe said Obama himself wrote a cheque to Clinton.

"When the two of them walked into the room, the room erupted,'' he said. "This campaign has ended. Hillary Clinton has said we've all got to get together.''

McAuliffe said after speaking, Clinton and Obama took questions ranging from helping with the debt to promoting a joint ticket.

The meeting was part of a two-day effort to show unity between the former rivals who competed fiercely for the Democratic presidential nomination.

Clinton spoke to two trade groups earlier Thursday before she introduced Obama to her most loyal fundraisers. Behind the scenes, the two sides were negotiating the extent of her future involvement in Obama's campaign.

"I am asking you to do everything you can to help elect Barack Obama,'' Clinton told the American Nurses Association, a 2.9-million member group that backed her candidacy. "I have debated him in more debates than I can remember and I have seen his passion and his determination and his grit and his grace. In his own life he has lived the American dream.''

Clinton and Obama plan to appear together for the first time since the end of the primary on Friday in symbolic Unity, N.H. -- where each got 107 votes in the state's January primary. Clinton won New Hampshire in an upset that set the stage for their long campaign, and it is now a critical battleground for the general election.

Obama told reporters Wednesday that he thinks she'll be extraordinarily effective in speaking for his candidacy and he'd like to have her campaigning for him as much as she can. "I think we can send Senator Clinton anywhere and she'll be effective,'' Obama said.

But the extent of her travel for Obama is not clear. Obama campaign manager David Plouffe said Wednesday that they have not scheduled any events after New Hampshire. "We don't have any specific knowledge of her schedule past Friday,'' Plouffe said.

Three Clinton confidants -- Cheryl Mills, Minyon Moore and Robert Barnett -- are in talks with Obama's campaign to work out details of her future involvement, including travel, her role at the national convention and resolution of her more than $20 million debt. Part of their argument is that Clinton can spend more time helping Obama if she isn't raising money to pay her bills.

Some Clinton supporters, including some of those at Thursday's fundraiser meeting, have been frustrated with Obama's efforts to help Clinton with her debt while they are raising even more money for him. In response, the Illinois senator has asked five of his top donors to coordinate an effort to do so.

"As those of you who were on the call yesterday heard, Barack has asked each of us to collect five or six cheques to help Senator Clinton repay the people who provided goods and services to her campaign,'' finance chair Penny Pritzker said Wednesday in an e-mail to Obama's national finance committee. "He made this request in the spirit of party unity. Senator Clinton has promised to do everything she can to help us beat John McCain.''

Clinton's debt includes $12 million of her own money. She has said she is not asking for help to pay back that portion.

Obama told reporters Wednesday he wouldn't send an e-mail asking his small-dollar contributors to donate to Clinton because "their budgets are tighter'' and they probably couldn't make much of a dent.

Clinton's encouragement came 19 days after she suspended her campaign and endorsed Obama. Since then, she has stayed largely out of sight at her home in New York and on vacation in the Hamptons, with brief public appearances for journalist Tim Russert's funeral and a high school commencement address. She returned to the Senate this week, and was roundly embraced by Democratic caucus members in front of news cameras.

An Associated Press-Yahoo News poll out Thursday shows Obama has won over slightly more than half of Clinton's former supporters. About a quarter of Clinton's backers say they will support McCain over Obama.