Obama, who just three years ago was serving in the Illinois Senate, took the first formal step Tuesday toward a presidential bid eagerly anticipated by some Democrats, creating a presidential exploratory committee. The move allows him to start raising money and begin building a campaign.

An Obama aide said the formal announcement is planned for the state capital, where Lincoln lived before becoming the nation's 16th president. No specific site was announced.

Springfield, with its Lincoln connections, would provide a symbolic backdrop for Obama, a Chicago Democrat who portrays himself as a uniter.

"It's not the magnitude of our problems that concerns me the most. It's the smallness of our politics," Obama said in a videotaped announcement e-mailed to his supporters Tuesday.

"America's faced big problems before. But today our leaders in Washington seem incapable of working together in a practical, common-sense way."

"We have to change our politics and come together around our common interests and concerns as Americans," Obama said, announcing his exploratory committee on his Web site, www.barackobama.com.

Announcing in Springfield would highlight the city's historical connections to Lincoln, who led the nation through the Civil War and the struggle to end slavery.

If successful, Obama would become the nation's first black president.

Obama, 45, has served just two years in the U.S. Senate, making him less experienced than many other presidential contenders, but that may not be a liability among voters frustrated by partisanship in Washington.

The senior senator from Illinois, Democrat Dick Durbin, welcomed Obama's decision, while noting "it's still a long journey to the White House."

"Barack Obama brings to this race a promise of reconciliation and a feeling of hope that America desperately needs," Durbin said.

Obama rose to political stardom after his speech at the Democratic National Convention in 2004. After that, his decade-old autobiography, "Dreams of My Father: A Story of Race and Inheritance," became a best-seller.

His second book, "The Audacity of Hope: Thoughts on Reclaiming the American Dream," was released last fall and helped generate even more attention as he raised money for Democratic candidates. Oprah Winfrey has endorsed him.

He's considered a top contender for the Democratic nomination, along with Sen. Hillary Rodham Clinton of New York, who is expected to make her announcement soon.

Other Democrats who have announced their intentions to run include 2004 vice presidential nominee John Edwards, former Iowa Gov. Tom Vilsack, Connecticut Sen. Chris Dodd and Ohio Rep. Dennis Kucinich.

Obama's decision may underline Iraq as the dominant issue in the 2008 campaign. Obama can appeal to the party's strong anti-war sentiment by contrasting his opposition to the conflict with the votes cast by Clinton and Edwards authorizing the 2003 invasion.

"He is the current candidate to be in the top billing as the anti-Hillary," said Larry Sabato, a political scientist at the University of Virginia. "He scrambles the field for Hillary in that he has the charisma and command of the national media to really challenge her."

Obama appears likely to start out well behind Clinton, and possibly Edwards, in fundraising and organizing. Both factors are certain to be important when voters start selecting the nominees early next year in a tightly compressed set of caucuses and primary elections.

"There is going to be a premium placed on who can raise a lot of money before the first primaries and caucuses begin," said Alan Abramowitz, a political scientist at Emory University. "That's where we know Hillary Clinton is going to have plenty of money. The question is, who else is going to have the money if she falters?"

Unlike Jesse Jackson, whose candidacies in 1984 and 1988 were mainly symbolic, Obama launches his exploration as a serious and plausible effort to elect a black candidate to the presidency.

That could complicate Clinton's plans because she was assumed to have a strong appeal to black voters, who were among the strongest supporters of her husband, Bill Clinton, when he was president. Those voters also constitute perhaps the most loyal element in the Democratic Party's base.

If Obama becomes a declared candidate and survives the early tests of the Iowa and Nevada caucuses and the New Hampshire primary, he may be in a position to challenge Clinton in the South Carolina primary, where a large black vote could be decisive.

"The idea of an African-American candidate is something that's appealing to a lot of people - a lot of Democrats certainly," said Abramowitz. "When he gets into a general election, are there some voters out there who would be reluctant to vote for a candidate just because he's African-American? Yeah, there probably are still some. ... Most of those people wouldn't vote for any Democrat, so I don't see it as an enormous handicap."

Obama's freshness on the national scene has its pluses and minuses, Sabato noted.

"The negative is that he may not be able to convince people that he has the experience to be president. The positive is that he has very little record to attack," Sabato said.

In New Hampshire, state Sen. Lou D'Allesandro, a prominent Democratic activist, said he doubted that Obama would be handicapped either by money problems or by difficulties in organizing for the nation's first primary.

"He may surprise people in that he may attract a new group of younger people into this process," said D'Allesandro. "As far as raising the money is concerned, if people think you're going to win, they're going to give you money."

Obama's revelations about his drug use in high school and college - contained in his first book - raise questions about whether his youthful behavior could come back to haunt him.

Many political experts doubt that his admissions would prove troublesome in the primary.

"I think the voters don't care very much. Clinton took a lot of that off of the table," said Andrew Smith, an independent pollster at the University of New Hampshire. "Plus, you have to remember that now the great bulk of voters out there are baby boomers - and they were all doing a lot of that sort of stuff back when they were in high school, so they can all relate to it."

Obama was born in Hawaii, where his parents had met in college. His father was Kenyan, and his mother was a white American. They divorced when he was 2. He was raised in Indonesia and Hawaii. He moved to Chicago in 1985, where he worked as a community organizer with a church-based group.

He is a graduate of Columbia University and Harvard Law School and was the first black president of the Harvard Law Review. After Harvard, Obama returned to Chicago to practice as a civil rights lawyer and to teach constitutional law at the University of Chicago.

He served in the Illinois Senate from 1997 to 2004, gaining a reputation as a consensus-builder with liberal stands on the issues.

Joining the U.S. Senate in 2005, he carefully tended to Illinois issues for the first year and insisted he had no higher aspirations. But in the second year, he began building his resume with several foreign trips as a member of the Senate Foreign Relations Committee, and he's been out in front of other Democrats as an outspoken proponent of ethics reform.

His wife, Michelle, also a Harvard Law School graduate, works as an administrator for the University of Chicago Hospitals. They have two children, Malia and Sasha.

Dori Meinert can be reached at 202-737-7686 or dori.meinert@copleydc.com. Finlays Lewis can be reached at 202-737-7683 or finlay.lewis@copleydc.com.