The hunt for voter fraud (search) has consumed considerable time leading up to the election. But after the polls close, the legal fights are likely to shift to how to deal with what could be millions of provisional ballots.

Legal fights have already been launched in more than three dozen states. In some cases, lawyers are fighting over a few thousand, a few hundred or sometimes even a handful of votes.

With the campaigns fearing the races will be so close, they do not want to leave anything to chance. But one experiment may prove more important than any other in this election — the nationwide provisional ballot (search) system. Federal law passed by Congress in 2002 now requires that every person who comes to vote who is not on a registration list be given a ballot, the legitimacy of which will be determined after the race.

David Boies (search), who represented Al Gore in the 2000 election recount that went before the U.S. Supreme Court, said he thinks provisional ballots will help prevent problems.

"If you'd had provisional ballots in Florida last time, thousands of people that were improperly struck from the rolls because their names were similar to that of a convicted felon would have been able to vote. So it's a great idea," Boies said.

Wilth millions of newly registered voters this time, the chance for mistakes grows, which means provisional ballots could prevent voters from being disenfranchised. But, said Doug Chapin, director of Electiononline.org, the provisional ballots system could create problems itself.

"The more new voters you have, the more uncertain the system is about how they will deal with a negotiating process. The more possiblities you have for error and [there] may be controversies on Election Day," Chapin said.

Republicans have already said they fear Democrats could use provisional ballots to cast fraudulent votes.

"They will want to claim, in the event that they may be behind, that virtually every provisional ballot, regardless of its color, size or shape, or where it was cast, should be counted," said Bush-Cheney campaign manager Marc Racicot (search).

Provisional ballots are unique. They are only counted when the margin of victory is smaller than the number of provisional ballots cast. Then, each ballot is scrutinized one at a time.

"One of the practical complications is that if the margin of victory is less than the number of provisional ballots, you're going to have to litigate each one of those provisional ballots and that'll take days," Boies said.

Another wrinkle that could emerge is that most states require provisional ballots to be cast in the proper voting precinct. If they are not, they are not counted.

Early voting means the election has already begun in 31 states. Some provisional ballots may already have been filled out. And with a host of other concerns about legal registration and fraud already dominating the election, international election observers have been invited to monitor events at the polls.

Click in the box near the top of the story to watch a report by FOX News' Major Garrett.