CHARLOTTESVILLE, Va. — President Obama on Wednesday provided counterprogramming for a second day to the Republican National Convention, mocking its proceedings and contrasting his agenda with what he called the “backward” positions of Mitt Romney.

“Pay a little attention to what’s happening in Tampa this week,” Mr. Obama told a boisterous crowd estimated at 6,500, many of them students at the University of Virginia here. When the audience loudly booed at the reference to the Republicans’ gathering, he said: “Don’t boo. Vote!”

While aides have said that Mr. Obama has not watched television coverage of the convention, in his speech he called it “a pretty entertaining show” with “wonderful things to say about me.” Citing a widely debunked Republican television ad claiming that Mr. Obama gutted work requirements for welfare recipients, the president said to laughter and applause, “Sometimes they just make things up.”

It was a repeat of the playful exchanges Mr. Obama had on Tuesday in similar rallies at college campuses in two other battleground states, Iowa and Colorado, as he campaigned for the support of young voters, a group that was crucial to his 2008 election. But the White House was quick to point out that in between his appearances, the president was receiving updates from federal officials on Hurricane Isaac, he and his advisers mindful especially on the seventh anniversary of Hurricane Katrina of the political perils of seeming insensitive to a natural disaster.