Hundreds spread out across Philadelphia afterward to knock on doors and pass out literature.
"Coming to a rally isn't the hard part," Obama told the crowd at Temple University. "I need 20,000 doors knocked on."
Two candidates facing tough races were on stage for the president's get-out-the-vote message: Allegheny County Executive Dan Onorato, who trails in the polls behind Republican state Attorney General Tom Corbett, and U.S. Rep. Joe Sestak, who is in a tight race with Republican Pat Toomey for a U.S. Senate seat.
Obama asked his audience to approach the midterm elections Tuesday with the same enthusiasm that brought him to the White House and a wave of Democrats to Congress in 2008.
"Two years ago, it wasn't about me," he said. "It was about you and this country. ... You cannot stop now."
Sestak warmed up the crowd before the president's arrival, telling the students that Democrats need to continue working to "heal and repair" the country.
"Make sure everyone knows about what's at stake in this election," he said. "You don't just vote once for change, you keep fighting for it."
Onorato said the elections are not only about a vote for candidates but for "a philosophy - which way do you want this country to go?"
Other Democrats were on hand including Gov. Ed Rendell, Philadelphia Mayor Michael Nutter, U.S. Sen. Robert Casey and outgoing five-term U.S. Sen. Arlen Specter, who lost to Sestak in the May primary.
A group of about 25 anti-Obama protesters, many waving "Don't Tread on Me" flags, stood outside an entrance to the university auditorium as students filed in.
Toomey planned events Saturday afternoon in West Chester and Blue Bell in suburban Philadelphia. Corbett had scheduled stops in Saint Clair, Hazleton and Williamsport, winding up with a chat with tailgaters at Penn State's football game in State College.
On Sunday, Toomey planned to attend rallies in Bucks and Delaware counties with Corbett and other candidates on the final day of what was billed as his "More Jobs, Less Government" tour. His campaign said he had been to 17 counties over the week "meeting with voters and sharing his vision for restoring fiscal responsibility and balance to Washington."