(CNN) -- Sen. Hillary Clinton embraced the role of underdog and vowed not to quit as she and her rival in the Democratic presidential contest, Sen. Barack Obama, stumped across Pennsylvania on Tuesday.
Sen. Hillary Cinton said Tuesday in Philadelphia, Pennsylvania, that she won't drop out of the race.
Entering to the theme song from the "Rocky" movies, Clinton compared herself to Rocky Balboa, the boxing hero played by Sylvester Stallone, during an address to the AFL-CIO in Philadelphia, Pennsylvania.
"Sen. Obama says he's getting tired of the campaign. His supporters say they want it to end," she said.
"Could you imagine if Rocky Balboa had gotten halfway up those art museum stairs and said, 'Well, I guess that's about far enough'? That's not the way it works," Clinton said, referring to a famous scene in the first "Rocky" movie. Watch Clinton compare herself to Rocky »
"Let me tell you something. When it comes to finishing the fight, Rocky and I have a lot in common. I never quit," she said.
Neither Clinton nor Obama will win the 2,024 delegates needed to capture the nomination outright, meaning the superdelegates probably will determine the Democratic nominee. Watch an analysis of the race »
Obama currently leads Clinton in delegates 1,625 to 1,486, according to CNN estimates. Obama also leads in the overall popular vote.
Clinton recently has fended off calls from prominent Obama supporters -- including Sen. Patrick Leahy of Vermont -- to drop out of the race. They said the battle will weaken the Democratic nominee before he or she gets a chance to take on the presumptive Republican candidate, Sen. John McCain.
In response to the suggestions, Clinton has accused the Illinois Democrat's campaign of trying to suppress the vote.
"I know that a lot of Sen. Obama's supporters have tried to stop this election before people have a chance to vote," Clinton said in an interview Monday night with WNCT-TV in Greenville, North Carolina.
The senator from New York has made similar remarks in Indiana, which has a May 3 primary, and in Montana, which votes June 3.
The Obama campaign called the charges "completely laughable." Obama said Tuesday that Clinton should stay in the race as long as she wants.
"As long as she is on the ballot in any state and she's got supporters who want to cast their ballot for her, that she has every right to stay in the race," Obama told NBC News.
"She has run a formidable race. I mean, we won 11 contests in a row and that didn't knock her out, and that's some tenacity on her part," he said.
House Speaker Nancy Pelosi also weighed in, saying in an interview that aired Tuesday that the protracted presidential race between the two Democratic candidates should be allowed to "run its course."
But the California Democrat also said her party must rally behind a candidate "a long time" before the national convention in August.
Pelosi recently received a letter from Clinton supporters criticizing her for suggesting that the party's superdelegates, which consist of elected and party officials, should vote for the candidate at the convention who has the most pledged delegates after the primaries.
But, Pelosi said, "We do not know what these next elections will do" over the next four to six weeks, with primaries in Pennsylvania, North Carolina and other states.
"Sen. Clinton may well be going to the convention as the nominee," she said.
In the ABC interview, Pelosi stuck by her assessment that it would be harmful to the party if it appeared the superdelegates overturned the will of the people. However, the speaker said, "The superdelegates have the right to vote their conscience and who they think will be the better president and who can win."
Pelosi's desire for a resolution before the convention appears to be shared by Senate Majority Leader Harry Reid, who, according to spokesman Jim Manley, called on the superdelegates "who have already made up their minds [to] declare their support by July 1."
Pelosi's comments come as the two Democratic presidential candidates continue to campaign in Pennsylvania. That state's April 22 contest is the next big event on the Democratic primary calendar.
Despite her portrayal as the underdog, a CNN "poll of polls" calculated Monday shows Clinton leading Obama 52 percent to 38 percent in the state, with 10 percent unsure.
The Pennsylvania poll of polls is an average of three polls -- American Research Group, Franklin and Marshall, and Quinnipiac -- conducted March 10 through 27.
Nationally, a CNN "poll of polls" has Obama leading 46 percent to 42 percent over Clinton, with 12 percent unsure. The national poll of polls is an average of four polls -- Gallup, NBC/Wall Street Journal, Pew and Fox/Opinion Dynamics -- conducted March 18 through 30.
While on the trail Tuesday, the candidates mostly kept their focus on the economy. Both said they would target the windfall profits oil companies earned from record-high gas prices and wanted to work to increase the nation's energy independence. Watch Obama talk about the 'American Dream' slipping away »
"I want to be honest with people. The only way we are going to deal with this problem is to reduce our consumption of oil," Obama said in Wilkes-Barre, Pennsylvania. E-mail to a friend
CNN's Emily Sherman and Alexander Mooney contributed to this report.