By John Whitesides, Political Correspondent
WASHINGTON, March 6 (Reuters) - An aide to Hillary Clinton likened Democratic presidential rival Barack Obama to independent prosecutor Ken Starr on Thursday, comparing criticism of her to the 1998 probe that led to President Bill Clinton's impeachment.
Clinton spokesman Howard Wolfson criticized Obama's promise to take a more aggressive stance with the New York senator after she won three of four states on Tuesday in their hard-fought battle for the Democratic nomination to face Republican John McCain in November's election.
"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 was the independent prosecutor who led the investigation of Bill Clinton, Hillary Clinton's husband, in a 1998 controversy that led to his impeachment on perjury and obstruction of justice charges by the House of Representatives and his subsequent acquittal in a Senate trial.
Starr's probe, which focused on Clinton's denials under oath about his sexual relations with White House intern Monica Lewinsky, came under heavy attack at the time from Democrats who called it politically motivated.
Obama, an Illinois senator, said on Wednesday he planned to step up his 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.
Obama's campaign quickly labeled the 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.
Obama and Clinton face a long battle for the nomination after Clinton's big comeback victories on Tuesday, just as she appeared to be on the verge of being knocked out of the race. Clinton announced she raised $4 million over the Internet since her big wins.
With 12 contests remaining, Clinton still faces an almost impossible 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 all would have to agree on the formats and timing of new contests, and Democratic Party chief Howard Dean reiterated he does not plan to intervene in the process.
"I think we may well have a clear-cut winner. I think we need to give the voters an opportunity to do that," he said on ABC's "Good Morning America." (Editing by David Alexander and David Wiessler) (For more about the U.S. political campaign, visit Reuters "Tales from the Trail: 2008" online at blogs.reuters.com/trail08/)