WASHINGTON - Imploring supporters to stick with him, President Obama acknowledged Tuesday that his reelection is not "a slam dunk" because of understandable public skepticism over the economy but said his campaign would put forward a vision aligned with the mood of the country.

Obama, addressing donors at a hotel near the White House, drew attention to his efforts to heal the economy, end the Iraq war, and overhaul health care but said: "All those things don't mean that much to somebody if they're still out of work right now or their house is still underwater by $100,000. So, yeah, this is going to be tough."

"We're going to have to fight for it. It's not going to be a slam dunk," he said. Obama said his campaign would pursue "the vision that is truest to our history and most representative of the core decency of the American people."

Obama spoke hours after his top campaign advisers said they were uncertain which Republican would emerge to challenge him next year but predicted a long GOP primary contest that they said would produce a weaker opponent in 2012.

Democrats have been targeting former Massachusetts Gov. Mitt Romney as the most likely GOP nominee but noted that former House Speaker Newt Gingrich's surge in the polls had made the Republican contest unpredictable.

Obama campaign officials said in a briefing that they expected a lengthy primary contest that would eventually hurt the party's nominee. They noted that only 15 percent of Republican convention delegates would be awarded by the end of February, making it likely that the contest would continue well into the spring.

Obama campaign strategist David Axelrod said the Republican candidates were "being tugged to the right every day. I think they're mortgaging themselves for the general [election] by tacking as far as they are."

He said that would make it more difficult for the nominee "to scramble back" to the center and appeal to a broader base of the electorate for November's election.

Obama campaign officials also claimed an organizational advantage over the GOP.

They said they had more staff on the ground in Iowa than the Republicans and had had about one million conversations with supporters and about 90,000 in-person meetings with volunteers since Obama began his reelection effort in April.