Barack Obama raised a record $55 million (27 million pounds) in February, beating rival Hillary Clinton's total and ensuring a big-spending battle for the Democratic presidential nomination in the months ahead.

Obama's haul, announced by aides on Thursday, was a fund-raising record for a single month. It trumped Clinton's $35 million in February and gave the Illinois senator some much needed good news after two critical losses in Ohio and Texas.

Clinton dodged a possible knockout blow in the presidential race with the wins over Obama on Tuesday, setting up a long and bruising fight for the Democratic nomination to face Republican John McCain in November's election.

The New York senator raised $4 million over the Internet since her big wins and $6 million since the month began, her campaign said.

Clinton spokesman Howard Wolfson criticized Obama's promise to be more aggressive in the aftermath of Tuesday's losses and likened him to independent prosecutor Ken Starr, a lightning rod for Democratic criticism during the 1998 probe that led to President Bill Clinton's impeachment.

"I for one do not believe that imitating Ken Starr is the way to win a Democratic primary election for president, but perhaps that theory will be tested," Wolfson told reporters.

Starr led an investigation of Bill Clinton, Hillary Clinton's husband, which focused on Clinton's denials under oath about his sexual relations with White House intern Monica Lewinsky.

The House of Representatives impeached Bill Clinton on perjury and obstruction of justice charges, but he was acquitted in a Senate trial. Starr's probe was attacked by Democrats as politically motivated.

Obama said on Wednesday he planned to step up criticism of Hillary Clinton and raise more questions about her national security credentials and issues like her refusal so far to release her recent personal tax returns.

Obama's comments were in response to what his campaign called Clinton's "slash-and-burn" tactics in the contests in Ohio and Texas, where she questioned his readiness to be commander in chief and lead on the economy.

"When Senator Obama was confronted with questions over whether he was ready to be commander in chief and steward of the economy, he chose not to address the questions but to attack Senator Clinton, and that's what we're pointing out," Wolfson said in a conference call with reporters.

'ABSURD'

Obama's campaign quickly labelled Wolfson's comments "absurd."

"After weeks of badgering the media to 'vet' Senator Obama, the Clinton campaign believes that they should be held to an entirely different standard," Obama spokesman Bill Burton said.

"We don't believe that expecting candidates for the presidency to disclose their tax returns somehow constitutes Ken Starr-tactics, but the kind of transparency and accountability that Americans are looking for," he said.

The Obama campaign said more than $54 million of his February donations were for the primary campaign battle with Clinton. It included more than 385,000 first-time contributors, bringing the total number of donors to more than 1 million.

With 12 contests remaining, Clinton still faces a difficult task in overcoming Obama's lead in pledged delegates who will choose the nominee at the convention.

But Obama also is unlikely to reach the 2,025 delegates needed to win, turning attention back to their efforts to woo 796 "superdelegates" - party officials and insiders - who are free to back any candidate and could make the difference in the race.

It also renews the focus on the states of Florida and Michigan, which were stripped of their delegates in a dispute with the national party but held unsanctioned contests anyway.

Talks have resumed about the possibility of a "do-over" in those two contests, which Clinton won even though no candidates campaigned. Obama was not even on the Michigan ballot. The two campaigns, the state parties and the national party would have to agree on the formats and timing of new contests.

Florida Sen. Bill Nelson, a Democrat, called for a new primary in the state and said the national party should pay for it. "We can't go on and ignore two of the largest and most important states," he said.

The next contests in the Democratic race are on Saturday in Wyoming, which has 12 delegates at stake, and Tuesday in Mississippi, which has 33 delegates at stake. The race will then have six weeks until the next battle in Pennsylvania on April 22.

Clinton, looking to emphasize national security, held a meeting in Washington with top military leaders and experts such as former U.N. Ambassador Richard Holbrooke, former Navy Secretary John Dalton and several retired officers who voiced their support.