On Wednesday, Jennifer L. Brunner, the Ohio secretary of state who is a Democrat, sent out an advisory to all local officials instructing them what to do if anyone who has lost a home to foreclosure shows up at the polls. If the address listed for such voters is no longer valid, and they moved outside the precinct, Ms. Brunner said, poll workers are instructed to send the voter to the polling place that corresponds to the voter’s new address. The voter will then be given a provisional ballot  special ballots that can be counted only after the voter’s eligibility is verified  at the proper polling place, the directive said.

The state requires that election officials send a notice to all registered voters verifying their address 60 days before an election to check the accuracy of the voter rolls. This month, Ms. Brunner ruled that an undeliverable notice will not be grounds enough on its own for a voter to be removed from the registration lists.

So far, election officials in Indiana, Kentucky, Missouri and Ohio have sent out notices to residents in select counties who have filed for a change of address but who have not updated their voter registration.

But the number of people who have moved, through foreclosure or for any other reason, far exceeds the number of people who have notified their election boards. In Ohio, 375,000 people filed change-of-address forms with the Postal Service, but when state officials sent them cards asking for updated registration information, only 24,000 responded. In Missouri, where 250,000 people notified the Postal Service of their move, only 22,000 told the election board.

Robin Carnahan, the Missouri secretary of state, and a Democrat, said that she is trying to get local election officials to increase the number of poll workers to deal with any confusion or challenges of voters.

In 2004, a Republican Party official challenged a large number of voters at a largely black precinct in Boone County, Mo., causing a backup. Such challenges can cause long lines at polling places if there are not enough poll workers to pull challenged voters out of line, or if the workers have to consult with higher-level election officials for each challenge.

State political parties have traditionally used the mail to determine which voters to challenge. By sending out mailings to voters likely to be of the opposite party, and then seeing which mailings are returned as undeliverable, they know whom to challenge at the polls for not living at their registered address. Using public lists of foreclosed homes, however, can save money by allowing a party to avoid sending out mailings.