Senator Obama of Illinois is moving toward a full-fledged run for the Democratic presidential nomination in 2008 by forming an exploratory committee and promising to make a final decision about a bid early next month.

Mr. Obama, 45, is a relative newcomer to Washington and to the list of potential presidential hopefuls for 2008, but his flirtation with a presidential campaign has excited Democrats looking for a charismatic candidate who is not weighed down by a long history of nettlesome congressional votes. In a video message posted yesterday on his political Web site, Mr. Obama, who opposed the invasion of Iraq from the outset, called that endeavor “a tragic and costly war that should never have been waged.” The first-term senator cited a litany of economic, environmental, and educational concerns, but focused more on the broader notion that Washington has become dysfunctional.

“It’s not the magnitude of our problems that concerns me the most. It’s the smallness of our politics,” Mr. Obama said. “Our leaders in Washington seem incapable of working together in a practical, common sense way. Politics has become so bitter and partisan, so gummed up by money and influence, that we can’t tackle the big problems that demand solutions.” Mr. Obama said he would spend the next few weeks consulting with friends and supporters before making an announcement on February 10. Democratic operatives said they are all but certain that the senator will run and that the testing-the-waters phase he has entered is a formality driven by the logistics of setting up for a formal announcement.

The likely entry of Mr. Obama is trouble for Senator Clinton, who was seen just months ago as a nearly prohibitive front-runner for the Democratic nomination. “If Obama gets hot, it’s a big problem for her and all indications are he could get hot,” a Democratic strategist, Joseph Trippi, said. While some analysts have said Mr. Obama could force lesser-known candidates out of the Democratic race by starving them of money and attention, Mr. Trippi took the opposite view, arguing that the senator could soften Mrs. Clinton’s numbers to the point where even the obscure hopefuls could gain traction. “It’s not just Obama who has a shot,” the strategist said. “By making the race more competitive with her, the race becomes more competitive for everyone.”

A spokesman for Mrs. Clinton, Howard Wolfson, declined to comment on Mr. Obama’s statement. Clinton advisers maintained an outward appearance of calm yesterday about Mr. Obama’s statement, which was not unexpected. However, behind the scenes, Mrs. Clinton and Mr. Obama have been intensely jockeying for the backing of New York’s leading Democratic fund-raisers, according to people close to the discussions. In recent days, donors thought to be flirting with support for Mr. Obama have been the focus of particular attention by the Clinton camp. Mrs. Clinton has made direct appeals to some who are wavering and, as she returned from a trip to Iraq and Afghanistan recently, called from Europe to shore up her support.

Mrs. Clinton has an obvious home-court advantage, as well as the ability to call on the longtime political allies of her husband, President Clinton. Mr. Obama has an enthusiastic, if smaller, band of backers in New York, led by some of the senator’s Harvard Law School classmates, including Michael Froman of Citigroup and Brian Mathis of Provident Group. Some prominent Democratic donors met Mr. Obama at an event in Manhattan last month hosted by a Manhattan financier who spent more than $25 million in support of Democratic causes in 2004, George Soros. A spokesman for Mr. Soros said yesterday that he has not made any decision yet about who he will back in 2008. Some at the December meeting are said to be squarely in Mrs. Clinton’s camp, but at least two big fund-raisers at the session, Hassan Nemazee of Nemazee Capital Corp. and Orin Kramer of Boston Provident Partners LP, have yet to declare their allegiances.

Members of Mr. Obama’s team contend that he can pull in donors not previously tapped by Democratic campaigns, especially among the younger set. “This is new and exciting,” one Obama backer said. “People will be queueing up to introduce him to their friends.”

One Washington veteran who appears to be moving closer to Mr. Obama’s camp is a former Senate majority leader, Thomas Daschle. “I think Barack Obama enters this contest in the very top tier along with Hillary. I don’t think there’s anybody else at this stage who would make that cut,” the South Dakota native said.

While Mrs. Clinton has been talking recently with many prominent Democrats about her likely presidential bid, Mr. Daschle said he wasn’t among those consulted. “I haven’t had a conversation with Senator Clinton in a little while,” he said. Mr. Daschle, who was mentioned for a time as a potential candidate himself, said he’d had “good conversations” with many of those likely to enter the race, but had “especially” positive discussions with Mr. Obama.

Asked if he was seriously considering backing Mr. Obama, the former majority leader said, “I am.” Mr. Daschle also has ties to Mr. Obama’s chief of staff, Peter Rouse, and a political adviser who could oversee Mr. Obama’s efforts in Iowa, Steve Hildebrand.

Mr. Obama’s early stance against the war has drawn support from liberal Democratic activists and bloggers known as the netroots. However, those hardcore Democrats may not be thrilled with the call for bipartisanship that was at the center of the senator’s announcement yesterday.

In addition, Mr. Obama’s claim to the anti-war left faces an immediate challenge from a former senator from North Carolina, John Edwards, who voted in favor of the war but has become an increasingly vocal critic of the effort. Mr. Edwards, who tried for the presidency in 2004 and wound up as the Democrats’ vice presidential nominee, recently called for a congressional effort to cut off funding for a troop surge planned by President Bush. Mr. Obama and Mrs. Clinton have questioned the surge, but neither has backed a congressional attempt to block it.

Meanwhile, on the Republican side of the ledger, Rep. Tom Tancredo of Colorado announced yesterday that he plans to form a committee to explore a presidential bid.

Mr. Tancredo, who is a vocal opponent of illegal immigration, said that on a recent visit to Iowa, voters convinced him that he is needed in the race for the White House.

“They believe that there is a void in this race that none of the other candidates are willing or able to fill,” he said, according to the Associated Press.

Two Republicans who have already launched exploratory bids for the White House, Mayor Giuliani and a former Massachusetts governor, Mitt Romney, also announced additions to their teams.