Sen. Hillary Rodham Clinton (D-N.Y.) is ratcheting up criticism of her two closest rivals in Iowa as new polls show continued fluidity in a close race in a vital state.

In a speech Monday in the first-in-the-nation caucus state, Clinton specifically targeted Sen. Barack Obama (Ill.) repeatedly. Clinton’s campaign said its candidate would try to “frame the primary election as a choice between a talker and a doer.”

While Clinton has clearly decided to take the fight to Obama and Edwards, her speech Monday focused on Obama, suggesting she continues to view the Illinois senator and what she sees as his thin record as her No. 1 target.

In an advance copy of her Iowa speech, which was delayed because of airport problems, Clinton said she is trying “to set the record straight.”

“The people of Iowa, I know, are good people who are trying very hard to make the right decision in this caucus,” Clinton said in prepared remarks. “But people can only act on what they know. And I’ve heard a lot of talk about turning the page, but what about the action to back it up?”

Without mentioning Obama by name, Clinton hits the senator for what she sees as the shortcomings of his healthcare plan, his failure to vote on the Kyl-Lieberman Iran resolution and, in a new charge, the many “present” votes Obama cast while he was in the Illinois state Senate.

“A president can’t vote ‘present,’ ” Clinton said. “A president can’t pick and choose which challenges he or she will face.”

As has often been the case this year when candidates come under attack, Obama tried to turn Clinton’s words into a way to raise campaign funds.

In an e-mail to supporters from Obama campaign manager David Plouffe, entitled “When Hillary attacks,” Obama’s campaign noted a weekend poll by The Des Moines Register that showed Obama edging to a narrow lead over Clinton.

“The emerging pattern is disturbing: As Senator Clinton’s poll numbers slide, the campaign of ‘inevitability’ becomes more desperate and negative by the day,” Plouffe wrote.

“It’s exactly one month until the Iowa caucuses, and Senator Clinton has promised that this is just the beginning of her negativity. She even quipped yesterday that attacking other Democrats is ‘the fun part’ of campaigning for the presidency,” he wrote.

Plouffe went on to say that if 10,000 people donate to Obama’s campaign in the next 48 hours, “it will show our opponents that when they attack Barack Obama, it literally makes our campaign stronger.”

The Obama campaign also announced a new website called “Hillary Attacks” that documents the criticisms aimed at Obama coming from the Clinton campaign.

Democratic candidates will have the opportunity to take new swipes at one another in what has become the key early contest for their party’s presidential nomination, when they take to Iowa’s radio airwaves Tuesday afternoon for a debate sponsored by National Public Radio (NPR) and Iowa Public Radio.

While a radio debate is likely to have fewer voters tuned in compared to nationally televised debates, analysts and consultants said the debate does offer the candidates a chance to work out some new lines.

Dennis Goldford, a political science professor at Drake University, said the candidates will likely use the debate as an opportunity to “sharpen some points of attack.”

Jenny Backus, a Democratic strategist, said the debate will not go unnoticed by Democratic supporters and donors both in Iowa and nationally. Because the state is so large, a number of voters spend a lot of time in their cars listening to the radio. And because it is being carried on NPR, Democrats and reporters across the country, who make up a large bloc of NPR listeners, could be tuned in.

“Anything you say or do in Iowa can be magnified,” Backus said. “It will just have something to do with setting the conventional wisdom.”

Backus added that the race in Iowa “is too close to call right now.”

Steve Elmendorf, a Democratic strategist who is supporting Clinton, said the tightened polls and sharpened knives are a natural result of a long campaign that is now about a month away from caucus day.

“I think you’re going to see a lot of back and forth,” Elmendorf said.