Senator Obama of Illinois is mulling a run for the Democratic presidential nomination in 2008, a bid that could prove the most serious challenge yet to the widely-acknowledged front-runner for the party’s nod, Senator Clinton.

In an appearance yesterday on NBC’s “Meet the Press,” Mr. Obama, 45, said he is considering a presidential campaign because the idea has been pressed on him repeatedly as he has traveled the country fund-raising for Democratic candidates.

“I don’t want to be coy about this,” Mr. Obama said. “Given the responses that I’ve been getting over the last several months, I have thought about the possibility.”

Mr. Obama, who won election to the Senate in 2004 and gained prominence that year as the keynote speaker at the Democratic National Convention, said he was focused for the moment on this fall’s congressional races. “After November 7, I’ll sit down and consider, and if at some point, I change my mind, I will make a public announcement and everybody will be able to go at me,” he said.

The senator’s indication that he may enter the presidential race is a change from the unequivocal disavowal of interest he offered earlier this year. In January, Mr. Obama said flatly that he would not be a candidate in 2008. “I will serve out my full six-year term,” he told NBC at that time.

Mr. Obama’s statement yesterday came following a whirlwind of flattering publicity he has received in connection with the publication of his new book, “The Audacity of Hope.” Last week’s issue of Time Magazine featured the Illinois senator on the cover and all but begged him to enter the race. In August, Mr. Obama, who has African roots, drew massive crowds of well-wishers as he toured Africa. He has also been in heavy demand to help Democrats fill their coffers for this year’s election.

A Democratic political analyst, Hank Sheinkopf, said he was not surprised that Mr. Obama has decided to give some thought to a presidential bid.

“It’s hard to say, ‘No,’ if 40,000 people are running down the street screaming your name,” Mr. Sheinkopf quipped, while scoffing at the Illinois senator’s chances of winning the nomination.

Polls show Mrs. Clinton to be the clear favorite for the Democratic nomination, but there has been steady pressure for an alternative candidate to emerge. Some of the impetus has come from the desire on the part of the press to see a hotly contested primary. However, some of the calls for a challenger have come from Democrats who contend that they support the former first lady but doubt her ability to win in the general election.

That concern is bolstered in part by poll numbers, such as a CNN survey taken in June, which found 47% of respondents said they would “definitely not vote for” Mrs. Clinton.

In a Quinnipiac University poll taken in March, Mr. Obama drew more a favorable response than did Mrs. Clinton. Mr. Obama received an average favorability score of 59.9 on a 100 point scale, while Mrs. Clinton came in at 50.4. However, 59% of the respondents said they didn’t know enough about Mr. Obama to rate him. Only 2% failed to rate Mrs. Clinton.

A spokesman for Mrs. Clinton, Howard Wolfson, declined to comment on Mr. Obama’s statement yesterday.

A Democratic activist in New Hampshire, Joan Ashwell, said yesterday that she welcomed the news that the Illinois senator may consider a bid.

“I would certainly look forward to hearing from him,” Ms. Ashwell said. “It’s his charisma, his presence, and he’s so articulate and so interesting to listen to.”

Ms. Ashwell chairs the Democratic committee in Strafford County, N.H., which hosted a dinner last month with the former governor of Virginia, Mark Warner. He was seen at the time as a possible alternative to Mrs. Clinton, but he announced recently that he will not run in 2008. A half dozen senators, a couple of governors, and several former officials have discussed running in 2008, but none has attracted the interest, or the opposition, that Mrs. Clinton has.

“I’m not sure if so much people want a counterpoint to Hillary Clinton, but people want to make sure there’s not just one choice put out there,” Ms. Ashwell said.

The Democratic mayor of Cedar Rapids, Iowa, Kathleen Halloran, said yesterday that Mr. Obama would have to work to catch up to other candidates who have invested considerable time in Iowa.

“It’s not a closed system,” Ms. Halloran said. “If he has enough traction and enough supporters, that deficit can be made up pretty quickly.”

However, a former Democratic chairman from South Carolina, Richard Harpootlian, said he does not think Mr. Obama can win the nomination, particularly because he has never served in executive office. “He’s a tremendously talented young man but I think he’s a little green at this point,” Mr. Harpootlian said. “I’m sure it’s flattering to hear this talk, but I think he needs to stay in the Senate awhile…He’s got to get re-elected first. That was John Edwards’s problem the last time around.”

Mr. Harpootlian, who was on board with Mr. Warner, said he isn’t sure where to look next. “Nobody in the process right now excites me,” he said.

Mr. Obama could have an advantage with anti-war Democrats because he has opposed the war from the outset and is not saddled with Mrs. Clinton’s 2002 vote to give President Bush permission to use force in Iraq.

Mrs. Clinton and Mr. Obama have similar voting records, though in 2005 he supported a bill to rein in class action lawsuits, while she voted against it.

While Mrs. Clinton would be the first female nominee for president, Mr. Obama would be the first of recent African descent, as his father was from Kenya.

“I think that Senator Obama rises above simple race politics,” a New Hampshire Democratic official, Raymond Buckley, said. “I think the color of his skin would be largely irrelevant to people.”

Mr. Buckley said he wasn’t sure Mr. Obama will run in 2008, but added, “He’s certainly doing a good job promoting his book.” It was ranked yesterday as the top-selling book on the Amazon.com Web site.

Mrs. Clinton, who is running this year for re-election to the Senate, has not announced a presidential campaign, though it is an open secret that she is considering a bid. During a debate yesterday on WABC-TV, she refused to pledge to serve out another full term in the Senate.

“I have made no decisions about any future plans. And if that is a concern to any voter they should factor that in to their decision on November 7th,” she said.