DES MOINES - Iowa is packed with presidential candidates and hundreds of campaign aides, advisers and contributors. Twenty-five hundred representatives of news organizations have been granted credentials to cover the caucuses on Thursday night, twice as many as in 2004. Rarely has a political event been so intensely anticipated as a decisive moment, at least on the Democratic side. (It is different for Republicans since many of their major candidates are not competing fully here).

What if at the end of Thursday, the three leading Democrats - John Edwards, Senator Hillary Rodham Clinton and Senator Barack Obama - are separated by a percentage point, or even less, leaving no one with the clear right of delivering a victory speech, or the burden of conceding? A number of polls going into the finals days that of have suggested that after all of this, the Democratic caucus on Thursday night will end up more or less as a tie.

In truth, amid all the endless permutations of possible outcomes that are being discussed - can Mrs. Clinton survive a third -place finish, or Mr. Edwards a second-place one? - aides are beginning to grapple with the frustrating possibility that all the time, money, and political skill invested here might prove to be for naught when it comes to identifying the candidate to beat in the primaries and winnowing down the top tier.

Rather than clarify the state of play and consolidate this crowded field a bit, an outcome like that would almost certainly muddle it further and potentially extend the time before Democrats know their nominee.

Since none of them would be judged a decisive loser, Mrs. Clinton, Mr. Edwards and Mr. Obama would all be able to go on to New Hampshire, no questions asked. It would be hard for any candidate to play the "I beat expectations game" and claim some sort of chimerical victory, much the way Bill Clinton proclaimed himself the winner after coming in second in New Hampshire in 1992. And you can bet this: the other Democrats in the race - Christopher J. Dodd, Joseph R. Biden Jr., Bill Richardson and Dennis Kucinich - would feel less of the morning-after-Iowa pressure to pull out.

New Hampshire, which for Democrats has seemed something like a stepchild in this year's nominating process given all the attention being paid to Iowa, would get a chance to have some real influence over the nomination. For 25 years, there has been debate and study about how the outcome in Iowa affects New Hampshire voters. This time around, because of the decision by the state's secretary of state, Bill Gardner, to set the New Hampshire primary on Jan. 8, voters would just have five days to examine the candidates and make their decision.

One of the bedrock political assumptions of the year - and certainly one that has informed Mrs. Clinton's campaign - is that winning Iowa and New Hampshire would set the table for sweeping the 20 or so states that vote or hold caucuses on Feb. 5, the day when many Democrats believe that their contest would effectively be decided. But if Iowans ended up being equally divided among what many party leaders view as an unusually strong cast of candidates, who is to say that voters in the Feb. 5 states will not be as well?

None of this is meant to suggest that an outcome like this would mean that what has taken place here over the past year was insignificant. Quite the contrary. Watching these candidates, both Democrats and Republicans, deliver their final speeches, take the last round of questions from Iowans and shake hands of supporters, it seemed hard to dispute that most of these candidates are much better at this than they were a year ago.

Mr. Obama's campaign manager, David Plouffe, an old Iowa caucus hand who has moved here to help out in the final days, said as much in explaining why he would be comfortable with even an inconclusive outcome. "The experience here in Iowa has been tremendous for the entire campaign," he said.