DES MOINES, Iowa -- In four days, a minuscule percentage of the voters of this small state will exert an outsized influence over the choice of the most powerful leader in the world.

And after a campaign that was at once the longest, earliest and most expensive in the 36-year history of the modern caucuses, no one knows who will prevail.

Yesterday, 10 candidates fanned out across the state offering their closing arguments in a campaign dominated, among the Democrats, by arguments on who would be the best agent of change and, among the Republicans, on who is the most authentic voice for conservative values.

The uncertainty is due not just to the limits of polling and the arcane nature of the caucus process, but also to the reality that after being the target of millions of dollars in ads and hundreds of days of campaigning, many Iowans have yet to make up their minds.

"I like him," Art Johnson, a retiree from Fort Dodge, said after listening to former New York City Mayor Rudolph W. Giuliani on Friday. Will he vote for him? "Possibly. I also like [former Tennessee Sen. Fred] Thompson and [former Arkansas Gov. Mike] Huckabee."

Earlier that day, after listening to a foreign policy speech by New Mexico Gov. Bill Richardson, Pam Hedges, of Des Moines, said she was leaning his way. But given the complex rules of the Democratic caucuses, she acknowledged there was a real chance that Mr. Richardson might not have enough support in her precinct to win any delegates.

In that case she and the supporters of other "non-viable" candidates will have the option of switching to someone else. Has she settled on a potential second option? "No," she said, adding, "I will by caucus night."

According to an ABC poll released last week, one-third of likely caucus goers said they might change their minds and 20 percent said there was a good chance that they would switch.

Turnout on Thursday is expected to be large, but even if it exceeds expectations, the percentage of voters taking advantage of the opportunity to exercise a vastly disproportionate influence on the country's political future is not expected to reach 10 percent, a number that casts the future of the caucuses into question.

At the top of the Democratic field, Sen. Hillary Rodham Clinton, of New York, Sen. Barack Obama, of Illinois, and former North Carolina Sen. John Edwards are locked in an apparently tight race. Hoping to crack that top three are Mr. Richardson, Sens. Joseph R. Biden Jr., of Delaware, Christopher J. Dodd, of Connecticut, and Rep. Dennis Kucinich, of Ohio.

On the Republican side, Mr. Huckabee appears to have surged to the lead, supplanting former Massachusetts Gov. Mitt Romney. In an appearance in West Des Moines Thursday, he drew a crowd estimated at 1,000, far more than the audience at a typical Romney event.

But his new prominence has also won him fierce attacks from the former front-runner, in an ad barrage attacking his record on government spending and suggesting that he is soft on immigration.

The budget hawks of the Club for Growth, led by Pat Toomey, a former congressman and GOP Senate candidate in Pennsylvania, has joined in the assault on the ordained Baptist minister. Mr. Huckabee has also been buffeted in the closing days of this drive by a series of mistakes he has made in discussing foreign policy.

Outside groups have also taken a run at Mr. Romney, with one new television ad deriding him for his switch on abortion from pro-choice to pro-life. Mr. Huckabee has particular appeal to the state's significant population of Christian conservatives.

The Atlantic magazine reported on its Web site, for example, that on Friday a group of national figures in the Christian right, including Dr. Tim LaHaye, the co-author of the hugely successful "Left Behind" series, were hosting a conference call for Iowa ministers.

Mr. Huckabee has been vastly outspent by Mr. Romney, but such contacts, in the description of one Romney aide, are part of a politically unconventional "viral network."

The Romney campaign hopes that its organizational strength, generally acknowledged as the deepest among the Republicans, can bring it back into contention with Mr. Huckabee.

In addition to losing his lead in Iowa, Mr. Romney is battling to retain his edge in New Hampshire, which votes five days after the caucuses. While attacking Mr. Huckabee here, Mr. Romney is airing ads criticizing the resurgent campaign for Arizona Sen. John McCain in New Hampshire.

Reacting to the Romney criticisms, Mr. McCain, who made one of his relatively rare campaign visits to Iowa last week, invoked his record as a Navy pilot as he told Fox News, "I'm familiar with tailspins and I think he's in one."

Mr. Huckabee also bristled at the renewed criticisms from Mr. Romney

"He's being dishonest about my record,' " he said yesterday. "When he talks about my record or John McCain's, he's making up stuff."

The assassination of Pakistani opposition leader Benazir Bhutto, discussion of which led to two misstatements by Mr. Huckabee, introduced another wild card into the Iowa deck.

Mr. McCain, the Republican candidate with the most extensive foreign policy resume, linked the Bhutto assassination and the release yesterday of a new audiotape from Osama bin Laden as reminders of the security challenges facing the next president.

The two events, he said in a statement, "are stark reminders that we are engaged in a worldwide conflict with Islamist extremism, and we cannot relent or waver."

It's unclear how much of an impact, if any, Mrs. Bhutto's death will have on caucus-goers but it gave several of the second-tier Democrats, including Mr. Biden, Mr. Dodd, and Mr. Richardson, openings to tout their foreign policy credentials in a race hat had been increasingly dominated by domestic issues such as health care.

Mrs. Clinton, in appearances across the state, cited the cited the tragedy as an example of the kinds of unforeseen crises that the next president will face. In doing so, she sought to buttress her argument that she is the leading Democrat who is most experienced and ready to lead.

Addressing the call for change that's echoed across the Democratic competition, she told an audience in Guthrie Center Thursday, "You don't get change by hoping for it" -- a dig at the "politics of hope" embraced by Mr. Obama.

Confronting the populist rhetoric of Mr. Edwards, she said, "You don't get change by demanding it. You get change by working hard every day."

Mr. Edwards continues to characterize Mrs. Clinton as a creature of a Washington culture dominated by insiders and special interests. He suggests that Mr. Obama is naive in saying that he would be able to overcome political partisanship by working across party lines and negotiate with powerful economic interests.

"It's a fantasy to think that they will give up their power," he told an audience in Indianola earlier this month."

For months, Mrs. Clinton appeared the chief target and rival for Mr. Obama. In recent days, however, his campaign has become increasingly critical of Mr. Edwards as well.

In a memo distributed to reporters Friday, his campaign manager, David Plouffe, painted Mr. Edwards as a hypocrite for arguing against special interests at the same time his campaign was being bolstered by the spending of outside groups nominally independent of his control.

Responding to the criticism yesterday, Mr. Edwards told the Associated Press, "Unlike other candidates, including Sen. Obama, I've never taken money from a PAC. If Sen. Obama and his campaign, want to focus on negative attacks they can do that, but that is not what I'm going to do."

The jockeying takes place amid what is, by all accounts, the most wide-open race here in twenty years. Looking at the results of the myriad polls in recent weeks, Mark Blumenthal wrote last week in an essay on the Web site, Pollster.com, "So if we take into account both the closeness of the Democratic race and all sources of potential poll error, we really have no idea who is truly 'ahead' at this point in the race. The polls are simply too blunt an instrument, especially given all the uncertainty about who will participate."

He noted that the art of accurately identifying "likely voters," a challenge in any survey is compounded by the small turnouts endemic to the caucus process in which voters are asked to attend community meetings that can last more than an hour.

An estimated 125,000 Democrats and 109,000 Republicans participated then. Citing research form the University of Iowa, David Yepsen, a columnist for the Des Moines Register and one of the state's leading political analysts, has written the Democratic turnout could reach 150,000 to175,000 this year with the GOP race attracting between 88,000 and 103,000. The eventual numbers are of more than academic interest in that a high turnout is generally seen as a good omen for Mr. Obama, and, to a lesser extent, Mrs. Clinton.

The Obama campaign hopes to energize voters, particularly younger voters, previously uninterested in politics. Mrs. Clinton's campaign hopes for an unprecedented turnout of women.

For Mr. Edwards, however, the conventional wisdom is that a smaller turnout would be better as his perceived strength lies with veterans of the caucus process.

The mystique of the caucus process, and Iowa's argument for its continuing special role, rests in the idea of ordinary citizens engaged by the presidential race at a face-to-face level.

To an extent, that image is true. It is common here to meet voters here who take the time to seek out the campaign events of as many candidates as possible. The White House hopefuls get used to fielding knowledgeable policy questions posed by ordinary citizens.

"It's so critically important -- what Iowa gets to do," said Mr. Dodd, praising the state's tradition as he embarked on a bus tour Friday. "In six days, Iowans get more say than any people in he country."

At the same time, however, the vast majority of Iowa voters don't care enough about their privileged role to bother to go to the caucuses.

Whatever the results Thursday, it's already safe to say of 2008's opening political rite, that seldom have so few decided so much while so many more stayed home and watched the Orange Bowl.