1:23 p.m. | Updated: Senator John McCain’s campaign said Friday morning that he will attend tonight’s debate with Senator Barack Obama at the University of Mississippi, reversing his earlier call to postpone the debate so he could participate in the Congressional negotiations over the $700 billion bailout plan for financial firms.

Mr. McCain had thrown debate preparation into turmoil on Wednesday afternoon after he announced that he intended to skip the debate in order to be in Washington for the negotiations. His campaign issued a statement Friday morning saying he was now “optimistic” that a bipartisan bailout agreement would be reached soon, citing “significant progress” in the talks.

The statement was sharply critical of Mr. Obama, who, like Mr. McCain, returned to Washington on Thursday to take part in the bailout talks. The statement portrayed Mr. Obama as unduly partisan and insufficiently concerned with protecting taxpayer interests in the bailout negotiations, while Mr. McCain was framed as the leader of House and Senate Republicans seeking to reach a compromise agreement.

“The difference between Barack Obama and John McCain was apparent during the White House meeting yesterday where Barack Obama’s priority was political posturing in his opening monologue defending the package as it stands,” said the McCain campaign statement.

“John McCain listened to all sides so he could help focus the debate on finding a bipartisan resolution that is in the interest of taxpayers and homeowners. The Democratic interests stood together in opposition to an agreement that would accommodate additional taxpayer protections.”

Senator Obama finished a round of telephone calls with Congressional leaders and the Treasury Secretary before leaving Washington on Friday morning. Mr. Obama landed in Tennessee about 1:20 p.m. Eastern, and was set to make his way to Mississippi for the debate. He is scheduled to arrive around 3:30 p.m. for a walk-through of the debate hall.

“My strong sense is that the best thing that I can do, rather than to inject presidential politics into some delicate negotiations, is to go down to Mississippi and explain to the American people what is going on and my vision for leading the country over the next four years,” Mr. Obama told reporters aboard his plane. “I’m looking forward to the debate and look forward after the debate to coming back to Washington and hopefully getting a package done.”

Moments after Mr. McCain announced that he would participate in the debate after all, the doors of his campaign plane were opened and the steps were down, as Mr. Obama’s 757 idled nearby on the runway at Ronald Reagan National Airport outside Washington, according to a pool report. Both planes were set to arrive here in Memphis on Friday afternoon.

Mr. Obama said he was encouraged by the Congressional negotiations underway on the government’s bailout package of the nation’s financial institutions, saying he was “optimistic” at the prospects for a deal.

“I think that there is real progress being made this morning and last night,” Mr. Obama said. “I think it’s important that the markets seem to be staying relatively calm at this point.”

Asked whether the White House meeting on Thursday was a mistake, Mr. Obama said: “I’m not sure that it was as productive as it could have been, but I think at this point, it’s important just to move forward.”

The discussion will resume later in Oxford, Miss., where the debate begins at 9 p.m. Eastern.

Elisabeth Bumiller contributed reporting from Washington.