OXFORD, Miss. — The presidential campaigns roared out of here Saturday in a pitched fight to make the case that the other candidate had lost the first presidential debate of the general election.

At the crack of dawn, the campaign of Sen. Barack Obama released a new advertisement criticizing Sen. John McCain for failing to utter the words "middle class" in the 90-minute debate, held Friday at the University of Mississippi here. By then, McCain had already produced and released an Internet video citing several instances in which Obama had said he agreed with his rival's positions.

The activity was part of a battle to shape public perceptions in the closing weeks of a razor-tight race. Both campaigns viewed the debates as a potential turning point, an opportunity for one side to finally break through in a race in which neither man has been able to sustain a statistically significant lead in polls.

Even as they sought to mold perceptions from the previous night, the campaigns were preparing for the next two debates, one on Thursday between Sen. Joseph R. Biden Jr. of Delaware and Gov. Sarah Palin of Alaska, and the other between McCain and Obama in a town-hall setting on Oct. 7.

Speaking with reporters on a conference call on Saturday morning, Obama's campaign manager, David Plouffe, called Palin "a gifted debater." Noting McCain's preference for town hall formats, and using the transparent, expectations-setting hyperbole common from both campaigns, Plouffe said he would be "thrilled" if "we can just escape relatively unscathed."

The positioning was in keeping with what is now a quadrennial rite in which the campaigns go full bore to convince the news media, and ultimately the public, that their candidate won. This often involves highlighting some supposedly fatal mistake by their opponent — the sighs of Al Gore at a 2000 debate; the first President George Bush's peek at his wristwatch while debating Bill Clinton in 1992.

In this case, McCain's campaign seized on a somewhat stammering reference Obama made to a bracelet he received from the parents of a soldier killed in Iraq after McCain spoke about one bequeathed to him. Obama's campaign sought to portray McCain as angry.

But the general sense was that the debate had not changed the landscape of the overall campaign. An anchorman on the Fox News Channel went so far as to tell a guest, Gov. Mike Huckabee of Arkansas, "They could have used you on the debate last night." Huckabee had won high marks for his quips in the Republican primary debates.