"Senator Obama speaks passionately on the campaign trail about empowering the American people," said the former first lady, who trails her rival in delegates won to date. "Today I am asking him to match those words with actions."
Obama has yet to declare his support or opposition, although his campaign has raised a number of procedural and legal questions about the most recent proposal for an early June primary in Michigan.
"The proposal offers a rerun for the state but not for all the voters," Bob Bauer, Obama's election lawyer, wrote in a memo during the day. He warned of the possibility of numerous legal challenges and embarrassment to the party.
Florida and Michigan both held primaries in January on a schedule that violated Democratic Party rules, and have been stripped of their convention delegates as a result.
Clinton made a hurriedly arranged trip to Michigan to dramatize her support for new primaries, at a time when some state party officials have been drafting legislation to hold a primary in June.
Clinton said nothing less than the outcome of the general election may be at stake in the dispute over the two states. "The road to a Democratic White House goes through Michigan and Florida," she said.
But there were strong political calculations at work, as well.
Clinton trails Obama in convention delegates after primaries and caucuses in more than 40 states, and her chances of catching up are remote at best.
Lopsided victories in second primaries in Florida and Michigan would help narrow the delegate deficit.
Even if she fell short, victories over Obama would strengthen her argument that party leaders who attend the convention as superdelegates should consider a candidate's ability to win in key states in the fall election before they pick a candidate.
Originally, Michigan was to have 128 delegates at stake in its primary; Florida's total was 185. Superdelegates swelled the totals.
Clinton won the renegade primaries in both states, although all the candidates had pledged not to campaign in either and Obama removed his name from the Michigan ballot.
Clinton referred to that in her brief appearances before members of an audience gathered in an AFSCME union building.
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"When others made the decision to remove their names from the ballot I didn't because I believe your voices should count," she said. "And that's why I've been saying we need to either count the votes that have already been cast in Michigan or Florida or have new full and fair elections."
Bauer's memo did not go as far as flatly opposing the proposal under consideration, but it cited numerous potential difficulties.
He said any revote would have to be approved by the Justice Department under the Voting Rights Act and noted that it would be paid for by private funds. He also warned of possible lawsuits by Democrats or independents who voted in last winter's Republican primary, and would be barred from the second primary as a result.
"In other words, the proposal offers a rerun for the state but not for all the voters," he wrote.
Adding to the pressure on Obama, two backers of Clinton - New Jersey Gov. Jon S. Corzine and Pennsylvania Gov. Ed Rendell - said Wednesday they have commitments for $12 million to pay for a Michigan primary. Among the 10 potential donors, five are major Clinton fundraisers listed on her Web site as "Hillraisers" and Roger Altman, who runs a private equity firm and is one of Clinton's economic advisers.
Both Michigan and Florida presumably are friendly territory for the New York senator. Michigan is home to large numbers of white blue-collar workers, many of whom have favored her in other primary states.
Obama's difficulty in reassuring Jewish voters about his support for Israel makes Florida problematic for him in a primary, as does the presence of large numbers of Hispanic voters.
Clinton's case was strengthened during the day when the two leaders of the Democratic rules committee issued a statement saying the emerging plan in Michigan was in keeping with party rules. The entire committee has yet to review the proposal.
But the clerk in Wayne County, which includes Detroit, cautioned that school board elections scheduled for May would make it difficult to hold a state primary in early June. Voting machines and ballot boxes "must remain sealed" until May 27, Cathy M. Garrett wrote to state Rep. Kathleen Law.
"While I understand the effort to make Michigan a significant voice in the presidential nominating process ... I have sincere concerns regarding the proposed 'do-over' primary election," Garrett wrote in a letter obtained by The Associated Press.
Plans for a re-vote in Florida collapsed over the weekend, leaving the fate of that state's delegation in doubt. To break the gridlock, state Sens. Steve Geller and Jeremy Ring proposed awarding half the state's delegates based on the popular vote in the Jan. 29 primary and the other half based on the popular vote cast in all states, excluding Michigan and Florida.