PHOENIX — Three days after the election, the outcome of several races remained a mystery in Arizona as officials struggle to count a record number of early and provisional ballots, many of them cast by voters who believed they had registered but whose names were not on the voter rolls at the polling place.

On Thursday, Secretary of State Ken Bennett revealed the magnitude of the situation: 631,274 votes remained uncounted, he said, more than in any presidential election in memory and enough to anger voting- and immigrant-rights advocates, who have called on the Justice Department to investigate. (By Friday, there were 524,633 uncounted ballots. There are 3.1 million registered voters in the state.)

The advocates, who have been staging nearly continuous protests outside the Maricopa County Tabulation and Election Center, where most of the votes are being tallied, have raised accusations of disenfranchisement, saying the same Latino voters they worked so diligently to register may have been disproportionately affected. Based on accounts they have been collecting since before the polls closed, among the 115,000 voters who cast provisional ballots in Maricopa County on Tuesday were many first-time minority voters who signed up to get their ballots by mail, but never did.