Sen. Barack Obama smiled as he was thanked by residents Nov. 22 outside the St. James Food Pantry in Chicago, where he spent the morning handing out Thanksgiving groceries. (AP/M. Spencer Green)

Sen. Hillary Rodham Clinton believes her biggest obstacle to winning the Democratic Party’s presidential nomination in 2008 could be Sen. Barack Obama.

Sources close to Ms. Clinton said she has been concerned that Mr. Obama could outdo the New York senator in getting support from the minority and liberal base of the Democratic Party. They said Ms. Clinton and her husband, former President Bill Clinton, have been discussing a strategy on how to deal with Mr. Obama and whether he could be persuaded to join a Clinton ticket.

“On paper, this man [Obama] should not be any threat,” a political strategist regarded as close to Ms. Clinton's team said. "He is too young and inexperienced. Yet, he exposes Hillary's weaknesses in a way that has people worried.”

The strategist said Mr. Obama could exploit several of Ms. Clinton’s weaknesses—Iraq and her profligate campaign spending. The strategist pointed to Mr. Obama's early opposition to the Iraq war while Ms. Clinton supported the U.S. invasion.

“I believe that it remains possible to salvage an acceptable outcome to this long and misguided war,” Mr. Obama told the Chicago Council on Global Affairs on Nov. 20. “But it will not be easy. For the fact is that there are no good options left in this war.”

Another weakness Mr. Obama could exploit is Ms. Clinton's huge spending in her 2006 re-election campaign for the Senate. Ms. Clinton has angered major contributors by spending more than $30 million—exceeding that of any other Senate candidate—against an unknown challenger.

For his part, Mr. Obama, 45, has sought to beef up his foreign policy and national security credentials, often appearing at the same venues as Ms. Clinton. With the help of such leading strategists as David Axelrod, Steve Hildebrand and David Plouffe, Mr. Obama, the son of a Kenyan father and a white mother, has presented himself as a man with fresh ideas who could reach out to whites as well as minority groups.

“I am new enough on the national political scene that I serve as a blank screen on which people of vastly different political stripes project their own views,” Mr. Obama, displaying unusual candor, said in his book “The Audacity of Hope.”

At this point, Mr. Obama, who has published two bestsellers and maintains a friendship with Oprah Winfrey, has the second highest recognition factor after Ms. Clinton, trailing the New York senator by 12 points in a recent Gallup poll of likely Democratic presidential candidates. Still, in what strategists said constituted the first trial run for 2008, the Illinois senator was deemed the most exciting candidate on the campaign trail and held a particular attraction for women.

“Obama is the new product on the market and the real test is whether he can survive long scrutiny," said John Gorman, chairman of the polling firm Opinion Dynamics.

In a poll Opinion Dynamics conducted for Fox News in late October, a presidential bid by Mr. Obama won 38 percent, three points behind that of Republican contender Sen. John McCain of Arizona. For his part, Mr. McCain held a six point lead over Ms. Clinton in any two-way race.

Already, several leading senators have encouraged Mr. Obama, a member of the Senate Foreign Relations and Veterans' Affairs committees, to test the waters for a presidential race. They include the No. 2 Democrat in the Senate, Sen. Richard Durbin of Illinois, who urged Mr. Obama to speak to audiences in Iowa, home to the first presidential caucuses.

“I think more people in Iowa are interested in his thought process about the future," Mr. Durbin said.

Mr. Obama is expected to decide on a presidential campaign in December. Aides said the senator has been discussing the issue with his family.

“Do I have something unique to bring to a presidential race that would justify putting my family in what everyone understands would be a grueling process?” Mr. Obama responded when asked whether he has decided to run.

Clinton advisers have been concerned that Mr. Obama, a proven fund raiser who represents an increasingly influential black leadership in Congress, could become the hope of every Democrat and Republican who wants to block her efforts to the White House in 2008. They said Ms. Clinton wants to avoid a bruising party nomination fight, particularly one against an African-American.

“He [Obama] wants to come where other people have already tread so that he knows basically what is going to be said in response to his policy,” said Larry Sabato, a leading political strategist who teaches at the University of Virginia. “He could be a liberal, or a moderate or a conservative. People really have no sense of him.”

The worst-case scenario, the sources said, would be a Clinton-Obama slugfest in the South, where the New York senator would seek support from black voters who had backed her husband more than a decade ago. But Clinton advisers don't believe she could compete against Mr. Obama in the black community, which comprises nearly 50 percent of the Democratic vote in the South.

“I can envision Hillary working out a deal with Obama in which he becomes a leading ally and even promised a major Cabinet post,” the strategist said. “The last thing Hillary wants is to face a popular black candidate for the Democratic nomination.”