Hillary Clinton plans to drop out of the Democratic presidential race this weekend and throw her support behind Barack Obama, closing out a hard-fought and protracted primary after her opponent clinched the nomination earlier this week  with an avalanche of superdelegates.

New York's congressional delegation will endorse Obama on Thursday, a move Rep. Charlie Rangel said was timed to their departure from Washington, rather than an effort to pressure Clinton to concede before Saturday.

A Clinton campaign e-mail sent out to supporters Wednesday night read "Saturday, I will extend my congratulations to Senator Obama and my support for his candidacy."

The e-mail from Clinton stated it "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."

The Clinton campaign announced late Wednesday that it would be hosting an event in Washington, D.C, to "thank her supporters and express her support for Senator Obama and party unity."

The campaign initially scheduled the rally for Friday, but later shifted it to Saturday "to accommodate more of Senator Clinton's supporters who want to attend."

One senior Clinton adviser told FOX News the New York senator and one-time favorite for the nomination told her campaign staff members Wednesday that Friday will be their last day, and that she plans to bow out of the race.

The announcement brought to an end the historic campaign pitting the first serious female candidate against the most viable black contender ever.

Clinton also told about 20 House Democratic supporters on a conference call Wednesday afternoon that it was "time to bring the party together."

According to a senior Democratic source on Capitol Hill, she acknowledged there were "two wings in the party right now," and it was her obligation to "unite them."

Congressional sources told FOX News three high-powered House Democrats leaned on Clinton to end her campaign this week, even though she was at first vague about the timeline for her departure.

The three Democrats who prodded Clinton to formulate and then announce a specific exit plan were, according to Democrats familiar with the situation, Reps. Charles Rangel of New York, Barney Frank of Massachusetts and Norm Dicks of Washington.

All three were on the conference call Clinton conducted with House Democrats.

The consensus among House Democrats was that Clinton had to decide what to do "sooner rather than later."

Early Wednesday, Rangel voiced displeasure with Clinton's speech on Tuesday because it failed to acknowledge Obama's historic achievement in capturing enough delegates to win the nomination.

Dissatisfaction with Clinton's speech led to intensified pressure for her to withdraw so the party could begin focusing on "unity."

And while Clinton pledged to make the moves to begin unifying the party, the lack of a specific date caused Rangel, Franks and Dicks to step up the pressure.

Democratic sources also have said Clinton will suspend her campaign rather than close it down entirely. By suspending her campaign, Clinton would retain nominal control of her delegates and could continue to raise money to pay off campaign debts. She also would allow late-primary states to finish up the process of electing pro-Clinton delegates to the August convention.

Clinton's Friday exit was foreshadowed early Wednesday when House Speaker Nancy Pelosi, Party Chairman Howard Dean and Senate Majority Leader Harry Reid sent a letter to uncommitted superdelegates urging them to endorse a candidate no later than Friday. Pelosi said it was clear Obama is the nominee, and that Democrats should rally around him.

Numerous Democratic sources told FOX News that Reid would never have put his name on that letter if he were not certain Clinton's campaign would soon be winding down.

As Obama secured the nomination with a tidal wave of superdelegate endorsements and later a victory in the final Democratic primary Tuesday night in Montana, Clinton notably did not concede or even recognize his delegate majority. That left many wondering how and when she would wind down her campaign.

When asked about being Obama's running mate on the conference call with lawmakers, Clinton said she "was not campaigning for the position but will do whatever she is asked to do to help the party win in November," a source told FOX News.

Sources said Clinton staffers are being paid in full through June 15.

FOX News' Major Garrett, Mosheh Oinounou and The Associated Press contributed to this report.