Allegheny County has scrapped a deal to buy electronic push-button voting machines and will instead buy 4,700 touch-screen units from a different supplier, Chief Executive Dan Onorato announced yesterday.

Not all of the machines can be in place for the May 16 primary, and the county is making plans to deal with possible long lines at polling places.

Mr. Onorato also criticized the federal law that is requiring the county to replace its 40-year-old mechanical lever machines.

"If it was up to me, I'd be using the lever machines," he said. "I think this is the biggest waste of federal money I've ever seen."

Mr. Onorato's announcement came less than six weeks before the May 16 primary, when counties across Pennsylvania must have new voting equipment in place or face legal action from the U.S. Justice Department under the Help America Vote Act.

Last week, Secretary of State Pedro A. Cortes, who oversees elections in Pennsylvania, told Mr. Onorato that the machines the county had planned to buy from Sequoia Voting Systems were unlikely to be certified in time for the primary because of software problems.

County officials reopened negotiations with Election Systems & Software, a Nebraska firm, for its iVotronic, a machine that resembles a bank ATM.

Allegheny County's purchase will cost $11.9 million, slightly more than the deal with Sequoia. A $12 million federal grant will cover the expense.

More than 20 counties -- including Beaver, Butler, Cambria, Greene, Mercer and Westmoreland -- also have selected the iVotronic, which has received both state and federal approval.

But the machine still has many critics. It has encountered technical problems in Miami-Dade County, Fla., home of some of the infamous voting problems that plagued the 2000 presidential election and pushed Congress to pass HAVA, the most sweeping voting law in a generation.

Because of the looming deadline, ES&S plans to supply each of the county's more than 1,300 voting precincts with at least one machine by the primary, although company officials hope to have at least two per precinct. The company will have all 4,700 machines in place by the November general election, which features high-profile races for U.S. Senate and governor.

Precincts that attract long lines during the primary will allow voters to use fill-in-the-bubble optical scan ballots as backups. The ballots then would be placed in secure boxes and taken to a central location for counting.

County officials preferred Sequoia's AVC Advantage machine because it more closely resembles the lever machines. Both units allow voters to see the entire ballot at once.

The iVotronic is much smaller, weighing less than 15 pounds. Voters scroll through various computer pages and touch a 15-inch diagonal screen to select their choices.

Mr. Onorato promised an "aggressive" educational campaign for voters and poll workers.

Before county officials finalize a deal with ES&S, the elections board must vote on it. The three-member board includes Mr. Onorato and County Council's two at-large members, Democrat John DeFazio and Republican Dave Fawcett.

The board will hold a public meeting tomorrow at 6 p.m. in the county courthouse.

Mr. DeFazio and Mr. Fawcett said they needed to gather more information before they decide what to do, but Mr. Fawcett said he was reluctant to support any computerized system without a paper trail that voters can check before casting their choices.

The iVotronic, like many touch-screen models, can be equipped with such a paper trail. State officials, however, have declined to approve that feature because of concerns about voter confidentiality.

An alternative is the optical scan unit, the backup machine for the May election. Many voting activists, both nationally and locally, have lined up behind that technology because of its paper component.

Local election officials in Pennsylvania, however, are moving away from the optical scanner, according to Douglas Hill, chairman of the County Commissioners Association of Pennsylvania. Mr. Hill said the machine's ballots can create confusion for voters, who accidentally select too many or too few candidates in some races, a problem called "undervoting" and "overvoting."

Pamela Smith, nationwide coordinator for California-based Verified Voting, said a growing number of local governments across the country now prefer optical scanners, partly because they have lower maintenance costs than touch-screen units like the iVotronic.

The ES&S machine is likely to face criticism from local voting activists at tomorrow's election board meeting. Past meetings have featured impassioned testimony about the potential dangers and limitations of computerized voting.

Paul O'Hanlon, an attorney with Pittsburgh's Disabilities Law Project, said the iVotronic fails recently expanded federal requirements for handicapped accessibility.

Collin Lynch, a graduate student in the University of Pittsburgh's Intelligent Systems Program and a member of VotePA, predicted that ES&S would have trouble meeting the May deadline.

"We've got six weeks to an election and we're talking about finishing a deal now and starting training?" he said.

Amanda Brown, a spokeswoman for ES&S, said the company, which has customers in 47 states, would deliver its machines on time.

One of the company's most high-profile clients is Miami-Dade County. It first used the iVotronic in 2002.

During a primary election that year, poll workers needed extra time to start the machines, delaying the opening of voting sites.

"It went horribly," said Sandy Wayland, president of the Miami-Dade Election Reform Coalition.

Two years later, the county brought in Douglas Jones, an associate professor of computer science at the University of Iowa, to check technical problems.

Dr. Jones found several program errors that interfered with the machine's electronic auditing capability. He said ES&S later addressed the issue, but the incident exposed limitations with state and federal certification testing for electronic voting technology.

"The effect of that error was to throw the entire record of the election into question," he said. "That bug should have been detected during rigorous testing."