AMES, Iowa — As they sprint toward the first votes of 2008, the leading Democratic presidential contenders are toeing a careful line between taking veiled shots at their opponents and risking the wrath of Iowa voters by “going negative” in the final days.

Senator Clinton took her message of change and experience to four Iowa cities yesterday, bashing the Bush administration with a mixture of outrage and humor while largely holding her fire on her chief rivals, Senator Obama and John Edwards.

“After seven long years of George Bush and Dick Cheney, starting Thursday we are taking our country back,” Mrs. Clinton told an overflow audience of 750 in Ames, drawing out her words for emphasis and eliciting laughter from the crowd.

Describing her experience as first lady in her husband’s administration, Mrs. Clinton pointedly defended her focus on achievements during the 1990s as a goalpost for future progress.

“When I talk about the 1990s, some of my opponents say, ‘Oh there she goes again. Talking about the past,'” she began. “It is not like I’m talking about ancient Rome. We are talking about 10 years. It is within our memory. So it ought to give us confidence that we know how to do this.”

She later attempted a subtle contrast with Mr. Obama, offered in a similar vein as when President Clinton suggested voters would “roll the dice” by electing him. “I’m not asking that you take me on a leap of faith,” she said. “I’m asking you to look at the evidence and the record.”

Mrs. Clinton frequently lightened the tone of her speech with jokes, including an ad-libbed riff that appeared to give new meaning to the idea of a “vast right-wing conspiracy.”

When feedback began sounding loudly from the speakers, she said, “I was in Muscatine yesterday in the middle of going on about the Bush administration, and the microphone completely died. I said, ‘I know they’re a little obsessed with me, but this is getting absurd.'”

Her voice raspy from near nonstop campaigning in recent weeks, Mrs. Clinton largely stuck to her main themes and made no mention of a Des Moines Register poll released today that showed her trailing Mr. Obama by seven points, 32% to 25%, heading into Thursday’s caucuses here. Her campaign has criticized the poll, which drew heavily on independent voters, and has instead touted two other surveys released by CNN and Zogby that give her a slight edge over the Illinois senator.

“Two polls out this morning indicate Senator Clinton is ahead,” the former first lady’s top Iowa backer, former Governor Tom Vilsack, told the Ames crowd, ignoring the Register poll. “Momentum is on our side. I can feel it.”

Mr. Edwards, who was virtually tied with Mrs. Clinton in the Register poll, also shrugged off the survey as he addressed a packed hall of Iowans in Ames.

“I don’t need a poll to tell me we’re moving ahead,” the former North Carolina senator said.

Mr. Edwards did not reference any of his rivals in his speech, but his broader message of “fight” and confrontation with entrenched interests was a clear rebuttal to Mr. Obama, who has focused more on unity. In an implicit shot at Mr. Obama, Mr. Edwards repeated his criticism that people who think change can occur through “making nice” are living in “never-never land.”

“In whose world?” he asked at one point. “Not in the real world. That is a complete and total fantasy. It will never happen.”

Mr. Obama swung through many of the same cities as Mrs. Clinton. He did not mention the Register poll, but his campaign was clearly buoyed, with aides looking to feed the story that the momentum is with him in the final days. He delivered his stump speech to a boisterous gymnasium crowd in Council Bluffs last night, indirectly deriding Mrs. Clinton and Mr. Edwards by telling voters that there is already too much “anger” and “partisanship” in Washington. More than 1,000 people packed the gym at the Iowa School for the Deaf, a campaign spokesman said, citing building management.

Mr. Obama also directly addressed undecided caucus-goers, asking at the beginning for a show of hands for who remained on the fence. “We’ve got some marks here – we’ve got some live ones,” he quipped after a smattering of hands went up.

All three top Democrats are planning whirlwind tours of the state in the final days of the campaign, but Mr. Edwards tried to one-up his opponents even in scheduling with a 36-hour “Marathon for the Middle Class” that includes stops at midnight, 2:15 a.m., and 5:15 a.m.

Already bombarded with constant political ads on Iowa television stations, some undecided caucus-goers have been keeping an equally torrid campaign pace, hopping from event to event to catch each candidate one last time. “I’ve done the whole barrage,” an art teacher from Ames, Laurie Olk, said. She said she saw Governor Richardson of New Mexico yesterday morning, Senator Biden of Delaware at noon, and Senator Obama last night.

“I have three yard signs — for Hillary, Richardson, and Edwards,” Ms. Olk said. She said she was leaning toward Mr. Edwards over Mrs. Clinton. “She has the drive, but he has the passion.”

Sylvia Munsen, a music education professor at Iowa State University, said she could almost recite Mr. Edwards’s biography by heart. “I’ve heard the mill story 100 times, or 300 times, or 500 times, if I’ve heard it once,” Ms. Munsen said, referring to Mr. Edwards’s retelling of his father’s life as a mill worker.

Several Iowans also said they approved of the tone of the Democratic speeches in the final days, where the candidates have avoided direct attacks on each other. “We’re smart enough to figure it out,” Ms. Munsen said of Mr. Edwards’s obvious but unnamed attempts to contrast his message with Mr. Obama’s. “The negativity — when that starts, I just tune out,” she said.