PITTSBURGH – Hillary Clinton, facing another must-win vote, this one in Pennsylvania, used images of Osama bin Laden and a nation at war on Monday to present a last-minute display of toughness and sharpen a contrast with Barack Obama, who spent the day telling voters he is better positioned to bring about change.

Tuesday’s Democratic presidential primary will bring to an end a bruising seven-week period that has seen both candidates take blows over misstatements and other problems, heightening the anxiety of Democratic Party leaders that the ongoing primary struggle will hurt their eventual nominee, even while presumptive Republican nominee John McCain consolidates his gains, unifies his party and prepares for the fall.

With most analysts expecting a Clinton win Tuesday, both campaigns engaged in furious spin to manage the expectations of the public and party leaders.

Obama conceded to a radio station that he will probably lose, but noted that he has significantly closed a 20 percentage point deficit in the state. Clinton, for her part, said she does not expect to win by much, and questioned Obama’s viability in the fall if he cannot win large swing states like Pennsylvania.

As a potential indicator of how the candidates viewed the outcome, Clinton scheduled a celebration for supporters in Philadelphia on Tuesday night, while Obama, an Illinois senator, was headed for Indiana and a rally in Evansville featuring singer John Mellencamp, whose endorsement was courted, in anticipation of the next big battle awaiting both candidates on May 6.

A frenetic day of cross-state appearances by Obama and Clinton marked the last full day of campaigning before an anticipated record number of Pennsylvania voters go to the polls for a primary, their ranks swelled by an increase in voter registration generated by the prolonged campaign. The race featured more than $16 million in spending primarily on TV ads, with Obama holding a 3-1 advantage over Clinton.

Both quickly snapped up opportunities for free TV on primary eve, no matter the sophistication level. Obama and Clinton taped an appearance on Comedy Central’s “The Daily Show” and Clinton was interviewed for “Countdown with Keith Olbermann” and “Larry King Live.” Both Democrats, along with McCain, also taped an introduction to World Wrestling Entertainment’s “Raw.”

Attempting to display toughness, Clinton’s campaign launched a final ad that displayed images of bin Laden, Pearl Harbor and the stock market crash while a narrator asks, “Who do you think has what it takes?”

Obama campaign officials labeled the ad “fear-mongering,” as they did in Ohio when Clinton unleashed a controversial TV ad that asked voters who was better prepared to handle a 3 a.m. emergency crisis call at the White House. And the Obama camp followed up with an ad posted on its Web site in which an announcer asks, “Who in times of challenge will unite us – not use fear and calculation to divide us?”

Clinton echoed the theme of her ad throughout appearances Monday in Scranton, Harrisburg, and, in Pittsburgh, where she was joined by her husband, former President Bill Clinton.

“It is the toughest job in the world and you have to be ready for anything,” Clinton told a crowd in Market Square in downtown Pittsburgh. “Two wars, stock market and oil prices, an economy in crisis. Well, if you can’t stand the heat, get out of the kitchen. And I’m very comfortable in that kitchen making those decisions and standing up for you because I know that’s what it’s going to take.”

For his part, Obama initially did little to help himself counter Clinton’s claims that the Illinois senator could not deal with hard questions and difficult issues. As he greeted voters at a diner in Scranton, Obama shrugged off a reporter’s question about foreign policy by saying, “Why can’t I just eat my waffle?”

Campaigning later in suburban Philadelphia, Obama sought a low-key election eve presence as he met with about three dozen people for a policy discussion outside Montgomery County Community College.

While Obama typically implies at his more raucous political rallies that presidents have a great ability to move the nation’s economy, he was more measured with his approach on the college campus.

“The economy is like an ocean liner,” he said. “If you steer it in the right direction, it might start off just going one or two degrees differently. But that one to two degrees, 20 years out, means you’ve avoided the big iceberg.”

Obama, who has not taken questions from reporters traveling with him for 10 days, gave his supporters some advice about the cameras at the start of his event.

“Just ignore them,” he said. “Pretend they’re not there.”

Clinton aides, just as they did prior to March 4 victories in the Ohio and Texas primaries, said a win for the New York senator in Pennsylvania should raise questions among voters in the remaining contests and undecided convention superdelegates of whether Obama – regardless of his spending – can win major, electoral vote-rich swing states in the fall against McCain.

Geoff Garin, Clinton’s message strategist, contended swing state voters, who he identified as blue collar, middle-income and non-college educated, are “voters with whom we’ve been very successful and Sen. Obama has not been in a variety of settings.”

Noting the increasingly negative tone of the campaign in its final days in Pennsylvania, Garin maintained the Obama campaign was “jeopardizing their brand” by focusing on criticisms of Clinton rather than a positive message surrounding his call for changing Washington and creating a new style of politics.

A loss in Pennsylvania, Garin said, “will set a different tone for the races that follow in North Carolina and Indiana.”

Obama started April with a 5-1 cash advantage over Clinton. Burdened by $10.3 million in debt, she had $9 million on hand for the primaries, while Obama had $42 million in the bank.

He aggressively used that money advantage to battle Clinton in Pennsylvania, where he wants to prove he can win over the kind of white, working-class voters who have been drawn to her in many earlier primaries.

David Axelrod, Obama’s top strategist, declined to say how much the campaign had spent in Pennsylvania. But he said one estimate of $11 million “sounds high.”

“We’re going to get our share of votes,” Axelrod said. “I don’t know what that share will be but I know that we’re better off today than we were six weeks ago when we arrived to the announcement from the Clinton campaign that she was unbeatable here and we were 20 points behind.”

But the Obama campaign remains a clear favorite in North Carolina, which holds its primary with Indiana on May 6. After a potential debate between the two fell apart, Axelrod said, “Now, we’re going to spend our time meeting voters in North Carolina and move on from there.”