Sequoia Voting Systems today will begin shipping its electronic voting machinery to Allegheny County, even though a series of examinations by the state this week found that the system has critical software problems.

Over two days of testing in Harrisburg, a Carnegie Mellon University computer science professor found a way to manipulate vote totals on Sequoia's machine, the AVC Advantage. He told company officials they would have to address the problem and come back for further tests.

Pennsylvania Secretary of State Pedro A. Cortes, who oversees elections for the state, told Allegheny County officials yesterday the Advantage could still receive state certification by the May 16 primary election.

If it doesn't, the county will have to find a replacement quickly or risk losing a $12 million federal grant.

"Obviously, they're concerned about the time frame," county Manager Jim Flynn said of Mr. Cortes' office. "So are we. There's a lot of work to be done over the next month and a half."

Mr. Flynn said Sequoia officials had told him they want to move ahead with bringing their machines here.

They have a tentative retest date of April 11, he said.

A Sequoia spokesman couldn't be reached for comment, but earlier this week the company's Pennsylvania representative said any programing hitches could be fixed by the primary election.

Michael Shamos, the Carnegie Mellon professor who examines voting systems for Pennsylvania, said the issues were related to recently updated technology that makes the Advantage accessible for handicapped voters, a requirement of the federal Help America Vote Act.

"They need some time to diagnose the problems, develop comprehensive fixes, and test the system thoroughly before seeking re-examination," he said in an e-mail message.

Montgomery County has been using the Advantage since 1996. It, too, must update its machines to satisfy the federal law.

Allegheny County is purchasing 2,800 Advantages at a cost of $11.8 million to replace its lever machines.