The campaigns of President Bush and Sen. John F. Kerry have tentatively settled on a package of three face-to-face debates that both sides view as a potentially decisive chance to sway huge audiences ahead of the Nov. 2 election, Democrats and Republicans said yesterday.

Bush's campaign opened the negotiations by urging just two sessions involving Bush and Kerry, but yielded to the full slate of debates that had been proposed by the Commission on Presidential Debates, according to people in both parties who were briefed on the negotiations.

No agreement will be final until the two sides agree on details for the format of a town-meeting-style debate that Bush at first resisted but now is willing to endorse, the party representatives said.

The debates will be spread over two weeks just before the hectic homestretch of a bitter contest, which had been tied for months until Bush recently opened a small lead in a number of national polls. The nominees will focus on foreign policy during the opening session, on Sept. 30 in Florida; they will take questions from undecided voters at the town-meeting-style debate Oct. 8 in Missouri; and they will conclude with a session on Oct. 13 in Arizona that will revolve around domestic issues.

Vice President Cheney and Democratic vice presidential nominee John Edwards will debate Oct. 5 in Ohio. Each of the four debates will begin at 9 p.m. Eastern time and will run 90 minutes.

The officials, who declined to be identified because they were not supposed to be discussing the matter with reporters, would not say when an agreement will be announced.

Both campaigns declined to comment on the state of negotiations. Bush-Cheney communications director Nicolle Devenish said: "The campaign maintains its position that it will not negotiate the terms of the debates in the press."

Kerry's campaign sees the debates as especially important, coming after a period in which he has been put on the defensive by the Bush campaign and its conservative allies. Polls paint a confusing picture of the state of the race, with some showing a virtual dead heat and others giving Bush a clear advantage. In many of the key battleground states, Bush appears in stronger shape than his challenger.

Bush's chief negotiator, former secretary of state James A. Baker III, agreed to add the third debate in part because of Missouri's importance as a swing state and because the president did not want to be portrayed as ducking his opponent, according to a source.

Under the commission's proposal, the participants for the town meeting will be undecided voters from the St. Louis metropolitan area who are chosen by the Gallup Organization.

"The Bush campaign didn't want to do the town hall because they really didn't trust the process for identifying uncommitted voters," said a Republican source familiar with the talks. "But things are going so well for them and so poorly for Kerry that they didn't want to give Kerry an opportunity to change the subject and say that Bush is afraid of debates. Bush not doing debates or dragging out the debate on debates could have been played by the Kerry campaign as arrogance."

A Democratic official involved in the process said the Kerry campaign worked to bring pressure on the Bush campaign through the news media, Republican donors and public officials in Missouri to go through with the town-hall debate. Bush won the state by three percentage points in 2000, and both sides expected it to be among the most closely contested swing states, although a number of polls show Bush ahead there now.

After reaching agreement on the broad outlines of the schedule, Baker and Kerry's lead negotiator, Democratic power broker Vernon E. Jordan Jr., were negotiating details of the town meeting. Officials indirectly involved said they believed that was the only element standing in the way of a final agreement.

The town-meeting debate is to be held at Washington University in St. Louis, which hosted debates in 1992 and 2000 and had been selected as a commission site in 1996, but lost out when President Bill Clinton agreed to only two debates. University officials had already completed expensive preparations for security, broadcast transmission and parking.

The two sides decided to reverse the commission's recommendation that the debates focus first on domestic policy and later on foreign policy, which the president's campaign sees as his strength. Jordan agreed, both sides said.

The nonpartisan commission has sponsored debates in each election since 1988, but candidates are not obligated to accept the commission's proposal. As negotiations continued, the commission issued an unusual letter Wednesday saying the campaigns must settle on a schedule by today for production and logistical deadlines to be met. In a nudge to the Bush campaign, the letter included a reference to the popularity of the town-hall format with the public.

Both sides have already begun portraying the opposing candidate as a tremendous debater, as part of the quadrennial ritual of trying to lower expectations for the nominees' performances. Kerry strategist Joe Lockhart told reporters during a conference call Friday that he would "challenge anyone to name a major debate that George Bush has been in where he hasn't been considered the winner."

Matthew Dowd, the Bush-Cheney campaign's chief strategist, said in an interview earlier this month that Kerry "is very formidable, and probably the best debater ever to run for president." "I'm not joking," Dowd added. "I think he's better than Cicero," the ancient Roman orator. "But I think it'll be a very good thing for the American public to see these two men stand side by side. You can't hide who you are."

Both campaigns agreed to the dates, locations and moderators proposed by the commission. Commission officials plan to begin moving equipment and other materials into place at the debate sites today, on the assumption that their plan will be embraced by the campaigns.

The Sept. 30 debate will be held at the University of Miami in Coral Gables and will be moderated by Jim Lehrer, anchor and executive editor of "The NewsHour" on PBS. The Oct. 8 town-hall debate will be moderated by Charles Gibson, co-anchor of ABC's "Good Morning America." The Oct 13 debate will be at Arizona State University in Tempe. The questioner will be Bob Schieffer, CBS News chief Washington correspondent and moderator of "Face the Nation."

The Oct. 5 vice presidential debate will be held at Case Western Reserve University in Cleveland and will be moderated by Gwen Ifill, senior correspondent of "The NewsHour" and moderator of PBS's "Washington Week."