Democrat Barack Obama worked to build up newly-gained momentum Sunday after he overtook Hillary Clinton in the fight for superdelegates whose votes will be decisive in choosing the Democratic Party's presidential nominee.

At least three Democratic superdelegates pledged to back the African-American senator Saturday -- one of them formerly in Clinton's column -- marking a new milestone in his quest to represent the party in November's presidential election.

With Clinton gaining one new endorsement, based on the RealClearPolitics count, Obama's total reached 274 to her 271.

It marked a rapid change of fortune for Clinton, who though trailing Obama in the committed delegates from the primaries had maintained a solid lead in superdelegates -- a select group of 795 of the party elite who cast votes for whomever they choose in the nominating contest.

And while neither candidate was acting overtly as if the race was over -- Obama was pitching for votes Saturday in Oregon ahead of its May 20 primary, while Clinton held a Mothers Day fund-raising event in New York -- the writing appeared on the wall for the former first lady.

"Despite what some in the media are saying, this race is not over," Clinton reportedly told her superdelegate supporters in a conference call Saturday, according to a TalkingPointsMemo reporter who listened in to the call.

"I'm winning Catholic voters and Hispanic voters and blue-collar workers and seniors, the kind of people Senator McCain will be fighting for in the general election," she pointed out in Charleston, West Virginia, which holds its primaries next.

US Senator John McCain of Arizona has all but secured the Republican Party's presidential nomination.

The new endorsements Saturday marked a clear reversal of fortune for Clinton, a New York senator and wife of former president Bill Clinton, who is seeking to become the first woman US president.

In early February, she had 90 more superdelegates in her corner than Obama, and although he slowly chipped away at her lead, just a week ago she was still ahead by 17.

But his convincing win in North Carolina and their photo-finish in Indiana on Tuesday left him with an unassailable lead in pledged delegates and opened the floodgates for superdelegates to flock to his side.

"I'm proud to support Barack Obama for president," Arizona House of Representatives member Harry Mitchell said in Chicago.

"Like the primary voters of my congressional district ... I am inspired by Barack's vision for America, his ability to unify our country and bring much-needed to change to Washington," added the Democrat, one of at least 10 superdelegates announcing their backing for Obama since Friday.

"I think he's the right guy to unify our party and our country," California superdelegate Edward Espinoza said on his website.

"I hold much respect for the Clintons and their contributions to this country. However, this race is clearly headed in one direction and it's time for us to coalesce around one candidate," Espinoza said.

With only six primaries now left in their marathon battle to face down McCain in November's presidential vote, Clinton's chances of beating Obama were extremely steep.

Based on the RealClearPolitics count, on Saturday Obama had a total of 1,865 of the 2,025 delegates needed to clinch the party's nomination, while Clinton trailed with 1,697.

He also had a solid lead in the popular vote, another key to the race.

In another ominous sign, national pollster Rasmussen Reports announced it was halting surveys. "The race is over ... Barack Obama will be the Democratic nominee," is said.

Clinton faced new pressure to bow out after making controversial remarks to USA Today newspaper Thursday about white voters not supporting Obama.

Clinton referenced polls that she said "found how Senator Obama's support among working, hard-working Americans, white Americans, is weakening again, and how whites in both states (Indiana and North Carolina) who had not completed college were supporting me."

Speaking in Oregon Saturday, Obama dismissed concerns that the party would be divided on racial lines.

"I know there's a lot of concern about division. Let me assure you, this party is going to be unified next November."