CHAPEL HILL -- Despite a 25-point lead in the polls, Barack Obama cannot take North Carolina's May 6 primary for granted, supporters and a local political scholar agreed Friday.

Obama will speak at a rally Monday night at the Smith Center, his first day back in the state since the Pennsylvania primary last week. The rally will begin at 9:30 p.m. Doors open at 7 p.m.

The event is free and open to the public, but tickets are required.

North Carolina is the largest of the nine primary contests left, with 115 pledged delegates.

In a telephone conference call Friday, Obama National Campaign Manager David Plouffe and former John Edwards National General Chairman Ed Turlington said the primary could decide the Democratic race.

"We've heard a lot from the Clinton campaign about winning the big primary states," Plouffe said. "They're behind right now. They need to win out here. We think the stakes are very high for both campaigns."

The Obama campaign announced the endorsement last week of 49 Edwards supporters in North Carolina.

In addition to Turlington, the list included David Price and other members of Congress, a former chief justice of the N.C. Supreme Court, former Edwards law partners and longtime friends.

Thursday night, the day after former President Bill Clinton visited Hillsborough (see story, Page A3), the mayors of Carrboro, Chapel Hill and Hillsborough hosted an Obama fundraiser.

Plouffe and Turlington did not answer a question Friday about whether Edwards himself would endorse Obama.

But Bill Leuchtenburg, the William Rand Kenan professor of history emeritus at UNC, said at this point an Edwards endorsement wouldn't mean as much in this state as it might elsewhere.

"If we assume, as I do, that Obama is going to carry North Carolina, John Edwards' endorsement would only be significant in swelling the margin," Leuchtenburg said. "It probably would be more significant in states that are closely divided."

Edwards may not have endorsed one of the candidates because he, too, is divided.

On many issues, including the war in Iraq, Edwards probably aligns more closely with Obama, Leuchtenburg said.

On health care, he aligns more closely with Sen. Hillary Clinton. Elizabeth Edwards has endorsed Clinton's health-care proposals.

Obama can't afford to ignore or seem to ignore North Carolina, despite his lead in the polls, because doing so would fuel the perception that he is elitist and doesn't have to court all voters, Leuchtenburg said.

Turlington is backing Obama because "I believe he's the right person to lead our country, take us in a new direction." He called the May 6 contest the most important Democratic primary in the state in at least 20 years.

Plouffe said Obama would emphasize the middle class in his economic message.

The senator supports free trade that protects workers and the environment, he said, citing last year's trade deal with Peru as an example. Obama and Clinton supported the deal. Edwards did not, comparing it to NAFTA which he said devastated his native state of South Carolina.

Clinton's aggressive campaigning could cut into Obama's lead, but Leuchtenburg still predicts an Obama victory by a margin in the "teens."

If Obama does win big, it will increase pressure on Clinton to bow out.

Edwards' staffers said they did not see that happening. Leuchtenburg agreed.

As for the possibility of an Obama-Clinton ticket come fall, the professor said don't scoff.

"There is a chance," he said.

The reason?

A significant number of Obama supporters say they would sooner vote for John McCain than Clinton. The same is true for some Clinton supporters, who say they would pick the Republican before Obama.

"There have been odder things that have happened," Leuchtenburg said.

John Kennedy picked Lyndon Johnson for his running mate after Johnson had spread word that JFK was "a very sick man" with Addison's disease, he said.

Ronald Reagan picked the first George Bush after Bush criticized Reagan's "voodoo economics."