Mr. Obama wanted domestic issues to come last; advisers said that they believed even before the start of the financial crisis that the election was most likely to turn on the state of the economy and that he wanted the final televised exchange to focus on those concerns. He has argued that Mr. McCain would continue the economic policies of President Bush.

Mr. McCain also wanted foreign policy topics to come first in the debates, his aides said, in the hope of capitalizing on his positive reputation on national security issues across party lines.

He wanted limits on the original format for the first and third debates, which had been nine topics with nine minutes of free-flowing debate on each one. Mr. Obama went along, though his aides did insist that at least several minutes of open-ended debate occur in each block of questioning, because they believe he does well in that format.

Now the candidates will be asked a question, each will give an answer of two minutes or less, and then they will mix it up for five additional minutes before moving on to the next question in the same format.

Obama aides also agreed to use lecterns at the first event, which Mr. McCain preferred; at the third debate, the two men will be seated at a round table, in the 10 o’clock and 2 o’clock positions, with the moderator at 6 o’clock.

McCain aides said that they were conscious of the fact that Mr. McCain has a prominent scar on one side of his face, and that they could not predict how prominent it would appear with the camera angles, lighting and make-up.

Image Senator John McCain, at a speech in Wisconsin on Friday, will go to Mississippi this week for the first of three debates with Senator Barack Obama. Credit... Todd Heisler/The New York Times

The debate formats were negotiated by Senator Lindsey Graham, Republican of South Carolina, representing the McCain campaign, and Representative Rahm Emanuel, Democrat of Illinois, for the Obama camp. A handful of aides from both camps were also involved, hammering out issues between themselves and then holding conference calls with members of the commission to reach final agreements, people involved in the process said.