"The evidence is overwhelming that when voters do not have access to technology that notifies them of ballot errors, many more ballots are left uncounted," said Meredith Bell-Platts, a voting-rights attorney with the ACLU.

Cuyahoga County, which includes Cleveland and has more than 1 million registered voters, plans to send all paper ballots from precincts to a central location to be scanned and counted.

The ACLU alleges that the optical-scan system and centralized vote tabulation would not give voters notice of ballot errors — such as voting for two candidates for one office.

Opponents of the system say scanning should be done immediately at the precinct level to alert voters to such errors and allow them to correct invalid ballots.

U.S. District Judge Kathleen O'Malley set a deadline of Feb. 4 for the Ohio secretary of state and the county elections board to respond to the ACLU and a hearing for the next day on the request for a preliminary injunction.

Secretary of State Jennifer Brunner, Ohio's top elections official, said the thrust of the ACLU's request would rule out the use of absentee ballots because those voters wouldn't know whether they had made an error or get a chance to correct it.

Brunner said it would difficult to go back to the prior touch-screen voting system in time for the primary because of staff training and system testing requirements.

"The ACLU is too late," she said.

Messages seeking comment were left for Cuyahoga County Prosecutor Bill Mason, whose office handles legal matters for the elections board. Jane Platten, director of the Cuyahoga County elections board, referred requests for comment to Mason's office.

When the lawsuit was filed, Mason said he would challenge its contentions. Mason said the optical-scan system is permitted under the Help America Vote Act passed by Congress in 2002 in response to the disputed 2000 presidential election.