A day after telling disappointed supporters that she needed some time to figure out what to do next, Senator Hillary Clinton has announced that she will endorse Democratic nominee Senator Barack Obama at an event in Washington, D.C. on Saturday. But after a hard fought campaign that ended with Obama's slim victory following Tuesday's final two primaries, Clinton still seems to be keeping her options open and has not yet agreed to release her delegates to Obama.

"On Saturday, I will extend my congratulations to Senator Obama and my support for his candidacy," Clinton wrote in an e-mail sent to supporters early Thursday morning. "This has been a long and hard-fought campaign, but as I have always said, my differences with Senator Obama are small compared to the differences we have with Senator McCain and the Republicans. I have said throughout the campaign that I would strongly support Senator Obama if he were the Democratic Party's nominee, and I intend to deliver on that promise."

Clinton faced harsh criticism from some quarters following her speech Tuesday night in New York, during which she congratulated Obama for his tough campaigning but did not concede that he had won the nomination or make reference to the historic nature of his victory. The New York Times reported that the decision to endorse Obama at the event on Saturday came after leading Democrats urged her on Wednesday to bow out of the race in order to allow the party to throw its support behind the first-term senator from Illinois.

At Saturday's rally, she is expected to concede defeat, congratulate Obama and proclaim him the party's nominee, the paper reported, adding that some of Clinton's fundraisers would be moving to the Obama campaign, while others were still holding back to see what Clinton plans to do next. By suspending but not ending her campaign, Clinton can continue to raise money as she tries to pay down the millions of dollars in debt her 16-month bid to become the first female president has accumulated.

The writing on the wall became clearer for Clinton on Wednesday morning, when four top Democrats, including party chairman Howard Dean, House Speaker Nancy Pelosi and Senator Harry Reid urged all uncommitted delegates to make their decisions by Friday.

"The voters have spoken," they said in a statement. "Democrats must now turn our full attention to the general election."

While talk has swirled for months about a possible Obama/Clinton ticket, it became clear Wednesday that the Illinois senator was casting a wider net by setting up a three-member vice-presidential selection committee that includes Caroline Kennedy. (Read more about what Obama's next steps might be here.)

Clinton said she'd speak on Saturday about how the party and her supporters now need to rally behind Obama. "The stakes are too high and the task before us too important to do otherwise," she wrote.