John McCain and Barack Obama have agreed to three presidential debates in the fall and one between their yet-to-be-announced running mates.

All four debates, which are being sponsored by the Commission on Presidential Debates, start at 9 p.m. ET and will last for about 90 minutes.

The first debate, on foreign policy and national security, will be held Sept. 26 at the University of Mississippi and moderated by Jim Lehrer, host of "The NewsHour" on PBS.

The second one will be a town hall debate moderated by NBC's Tom Brokaw on Oct. 7 at Belmont University in Nashville. All the questions will come from the audience or the Internet.

The third debate, on domestic and economic policy, will be held Oct. 15 at Hofstra University in New York. CBS' Bob Schieffer will moderate that one.

The vice presidential debate will be moderated by PBS journalist Gwen Ifill and held Oct. 2 at Washington University in St. Louis. The debate formate won't be resolved until the vice presidential nominees are chosen.

Obama is expected to announce his vice presidential pick as early as Thursday. McCain plans to reveal his choice Aug. 29, the day after the Democratic National Convention.

McCain wanted to challenge Obama in several Lincoln-Douglas-style debates but the Obama camp countered with other ideas and no resolution could be reached. Obama's campaign has said these standard meetings will likely be the only ones.