“I don’t believe we have an agreement,” he announced to an enormous press corps crowded under the portico of the West Wing entrance. Mr. Shelby then waved what he said were five pages of letters from the leading economists in the United States, from Harvard, Yale, MIT and the University of Chicago, who he said viewed Mr. Paulson’s plan as a “bad plan” that would create more problems than it would solve.

Mr. Shelby said there were “a lot of different opinions” expressed at the meeting, and that Mr. McCain and Mr. Obama conducted themselves as senators who “were very courteous to each other and very respectful.”

As the afternoon continued, the senator began a series of interviews with the television networks to be aired Thursday evening and his campaign gave indications that he would leave on Friday morning for the debate in Mississippi.

Later in the day, Mr. McCain held out the possibility that he would still attend the debate although his campaign had made no formal plans.

“I’m hopeful,” Mr. McCain told Charlie Gibson in an interview on ABC News Thursday evening. “I’m very hopeful that we can. I believe it’s very possible that we could get an agreement in time for me to fly to Mississippi.”

Hours earlier, the Republican governor of Mississippi told reporters that he expected the event to take place at the University of Mississippi, and a representative of his campaign participated in a technical walk-through of the debate hall in Mississippi on Thursday afternoon as the moderator, Jim Lehrer of PBS, did his preparation.In a morning speech in New York, Mr. McCain said “a crisis calls for all hands on deck.” He formally suspended his campaign, and aides added that he intended to carry through with his call to skip the debate.

“With so much on the line, for America and the world, the debate that matters most right now is taking place in the United States Capitol  and I intend to join it,” Mr. McCain said.