WASHINGTON — Democratic presidential hopeful Hillary Rodham Clinton's campaign hammered rival Barack Obama yesterday for refusing to reaffirm his commitment to accept public financing in the general election, a development a top aide criticized as "a pretty big flip-flop" and an opening for Republican attack.

Clinton hasn't acknowledged that Obama is likely to be the Democratic nominee — she says she is — and she also hasn't promised to accept public financing herself. The issue, Clinton spokesman Howard Wolfson says, is that Obama made a campaign pledge but now won't promise to keep it.

The Clinton offensive is an effort to raise questions about the Illinois senator and dent his momentum as the campaign heads into another important primary tomorrow, this time in Wisconsin. The New York senator also has aired TV ads that blast Obama for refusing to agree to a debate in the Badger State, where a Real ClearPolitics.com average of three recent polls shows Obama with a lead of 4 percentage points.

Anthony Corrado, a political scientist at Colby College in Maine and an expert on money in politics, doubts that campaign finance promises or debate schedules will resonate with many voters. "At this point, it's a process issue," he says.

The dispute has forged a rare alliance between Clinton and Republican John McCain. McCain, the presumptive GOP presidential nominee, told audiences in Wisconsin that he would honor his pledge to accept public financing as a candidate, assuming his opponent does the same.

"I expect Sen. Obama to keep his word to the American people as well," the Arizona senator said.

Obama's chief strategist, David Axelrod, said yesterday on CBS' "Face the Nation" that it was premature to discuss what the campaign would do.

"We're not backing away," Axelrod said. "What Sen. Obama said is, once the nomination is secured, we will sit down with Sen. McCain as the nominee, and we will talk this through."

Last fall, the Midwest Democracy Network, a nonpartisan alliance of civic groups from five Midwestern states, released a questionnaire that asked candidates if they would "agree to forgo private funding in the general election campaign" if "your major opponents agree." Obama's response: "Yes."

He then described himself as "a longtime advocate for public financing of campaigns combined with free television and radio time as a way to reduce the influence of moneyed special interests."

Now, however, it's clear that accepting $85 million in public funding and agreeing to eschew private fundraising would mean giving up an enormous money edge. Obama's campaign raised more than $102 million last year and took in about $1 million a day in January, according to campaign manager David Plouffe.

McCain raised about $41 million in 2007 and ended the year with less than $3 million in the bank.

Agreeing to public financing wouldn't necessarily reduce the amount of money contributed or spent on the 2008 campaign, Corrado notes. The Democratic and Republican national committees can raise unlimited amounts of money to spend on a candidate's behalf, although the expenditures must be independent of the campaign's control.

In Wisconsin yesterday, a snowstorm forced Clinton to cancel two of her three scheduled appearances. Instead, she toured a grocery store in a Hispanic neighborhood of Milwaukee and visited Miss Katie's Diner near Marquette University.

The weather also prompted Obama to scrap a town hall in Kaukauna, his only scheduled public appearance of the day.

Obama also flew to Raleigh, N.C., to hold a meeting with former rival John Edwards, who amassed 26 delegates before dropping out of the race last month. He hasn't yet made an endorsement between the remaining contenders.