Diebold Inc., a multibillion dollar company that soon may sell 5,600 touch-screen voting machines to Allegheny County, has seen its share of public relations nightmares.

In 2003, then-chief executive officer Wally O'Dell -- a top fund-raiser for President Bush's re-election campaign -- sent out a letter to Ohio Republicans promising that he was "committed to helping Ohio deliver its electoral votes to the President next year."

Over the next several years, some computer experts and election officials pointed out potential security flaws with the company's machines, and cries of conspiracy and fraud circulated in the press and on the Internet.

Diebold, based in North Canton, Ohio, reacted by ordering all employees involved with its elections division, including Mr. O'Dell and other top company officials, to refrain from participating in any political activities beyond voting. Its machines also performed just as well, if not better, than those built by competitors.

But the company's mishaps have forced it into an uncomfortable spotlight, just as local governments across the country are upgrading their voting equipment to meet the requirements of a 4-year-old federal law.

Even some critics acknowledge that the extra attention isn't necessarily fair.

"Diebold is no worse than any of the others," said David L. Dill, a professor of computer science at Stanford University and founder of the Verified Voting Foundation. "I would be equally disappointed if Allegheny County and other counties bought another type of touch-screen."

Dr. Dill is one of a sizeable group of computer experts who have doubts about the reliability of touch-screen machines. They often prefer optical scanners, which use fill-in-the-blank ballots that resemble standardized tests and leave a lengthy paper trail.

Yet many elections officials, including those in Allegheny County, rave about Diebold's touch-screen machines. David Bear, a company spokesman, thinks some computer specialists don't understand the election environment.

"The goal is to be easy enough for voters to use, easy enough for poll workers to operate and affordable enough for taxpayers," he said. "I think some people are allowing 'perfect' to be the death of 'good.' "

The company has told Allegheny County that it could deliver 5,600 machines by the May 16 primary election, at a cost of $11.9 million. But the county's elections board, which meets Tuesday, needs to decide soon.

If the county doesn't act, it could lose a $12 million federal grant. No other company has pledged to deliver machines by the primary.

Founded in 1859 in Cincinnati, Diebold made a name for itself building safes. It now is a major supplier of ATMs and security systems for banks. It has 14,000 employees worldwide and its revenues reached $2.6 billion last year, according to Michael Jacobsen, director of corporate communications.

The company didn't enter the voting machine market until 2002, when it acquired Global Election Systems of Texas.

That year, Congress passed the Help America Vote Act, a response to the chaotic aftermath of the 2000 presidential election in Florida. The law, known as HAVA, calls on local governments to acquire new voting machines that meet strict standards, such as handicapped accessibility. The deadline is this year.

HAVA also set aside more than $3 billion in aid, a potential windfall for dozens of companies, including Diebold. From 2004 to 2005, revenues for Diebold's elections division jumped from about $90 million to $140 million, Mr. Jacobsen said.

It now has 100,000 touch-screen machines deployed in 37 states.

But a few setbacks have captured the most attention, particularly a run-in with California's former secretary of state, Kevin Shelley.

During the state's 2004 March primary election, four counties used Diebold's AccuVote-TSX, the same model being considered by Allegheny County. In San Diego County, more than 500 of 1,700 polling places failed to open on time because some elections workers had trouble operating part of the system. No votes were affected, although officials don't know how many people left without voting.

The problem was easy to fix, but it took time for computer troubleshooters to contact all the polling places that had difficulties, said Mikel Haas, the county's registrar of voters.

"Once everything was up and running, it went smoothly," he said.

None of the other counties experienced problems with the TSX.

"It worked beautifully, and the voters loved the machines," said Deborah Seiler, elections manager for Solano County, part of the San Francisco Bay Area. "I would argue that those are probably the best machines on the market now."

But a state investigation accused Diebold of threatening the results of the election with last-minute changes to its systems and the use of uncertified software. Mr. Shelley called the company's actions "reprehensible."

He temporarily decertified all touch-screen machines in the state and ordered the four counties using the TSX to rely on paper ballots until Diebold completed a new round of tests. The state also sued Diebold, and the company eventually paid a $2.6 million settlement.

Mr. Bear said the company paid the money as a way of moving forward, and he described the use of uncertified software as a misunderstanding, not an attempt to deceive state officials.

Last year, the TSX passed a new test performed by the state. Its memory card now is awaiting approval by the federal government, according to Jennifer Kerns, spokeswoman for California's current secretary of state.

Diebold recently encountered more bad publicity in North Carolina. Late last year, the company announced it wouldn't sell products there because state officials wanted detailed information about all software used in voting machines. The TSX partially relies on Microsoft Windows, and, under copyright laws, Diebold is limited in how much information it can share.

North Carolina's strict law stems from the last presidential election, when one machine, a UniLect Patriot, in Carteret County lost almost 4,500 votes.

Since the summer of last year, officials in Allegheny County have considered voting systems from eight companies. The Department of Administrative Services is advising the three-member elections board, which includes county Chief Executive Dan Onorato, to select the TSX.

"Obviously we've read a lot of the allegations that people are talking about," Angela Chan, the department's deputy director, told the elections board last week. "Obviously we cannot base our decision on hearsay or what's on the Internet."

But, until this new generation of voting machines holds up in several elections, doubts will linger. There have been no reported instances of fraud. That doesn't comfort some people, like Verified Voting's Dr. Dill.

"It would be very, very hard to prove," he said of potential attempts to tamper with elections. "Every computer scientist I talk to reports a queasy feeling when voting on these machines."