In less than five months, Pennsylvania voters are likely to be pulling levers and punching holes on aging voting machines for the last time.

They won't be alone. Across the country, local governments are beginning to replace or upgrade their voting machines to be ready for the next election involving candidates at the federal level. In Pennsylvania, that election will be May's primary.

But serious questions remain about whether the state's 67 counties will have enough time to put new machines in place.

At stake is more than $3 billion in federal aid set aside by the Help America Vote Act, legislation that grew out of the disputed 2000 presidential vote in Florida and a chaotic array of hanging, dimpled and pregnant chads.

Pennsylvania's share of the money is $136 million. Counties that replace their machines will receive at least $8,000 per polling precinct, and more if they meet federal guidelines for providing voter education and handicapped-accessible precincts.

Allegheny County, which must replace 2,800 lever machines that have been in use since the 1960s, could get as much as $12.5 million, according to Mark Wolosik, manager of the elections division.

This month, the state closed the bidding process for companies hoping to sell a new generation of high-tech voting systems that display ballots on touch-screen computer monitors. The Pennsylvania Department of State is now testing machines from more than a dozen companies.

Officials hope to have a list of certified machines by the end of the summer, but that won't be an easy deadline to meet.

"There isn't physically time to do all the exams necessary," said Michael Shamos, a professor of computer science at Carnegie Mellon University who runs testing for the state.

The machines also must be certified by the federal government.

In the meantime, all county election directors can do is wait for the state's list to be published.

"It's very frustrating. It's going to be more frustrating as the clock keeps ticking," Mercer County Elections Director Tom Rookey said. "It's like having your foot in a bear trap."

Mercer County voters are familiar with some of the problems that can affect touch-screen systems. In November, election officials there incorrectly programmed their UniLect Patriot machines, and the county had a presidential undervote of greater than 7 percent. That means for every 100 votes cast, seven failed to register a vote for a presidential candidate. A normal undervote, nationwide, is 1 percent to 3 percent.

As new voting systems have increased in popularity since the 2000 election, a growing number of computer scientists and political activists have started expressing concerns about the possibilities of widespread malfunctions, or, even worse, fraud.

To date, there has been no proof of wrongdoing involving computerized voting, but some experts still are worried about the possibility that determined computer hackers could find a way to upset an election. Many activists are calling for new machines to have paper trails that voters and election officials can use to check results.

Nearly half of all states have enacted legislation that requires computerized voting machines to use paper, and similar bills are making their way through both the U.S. House of Representatives and the Senate.

A bill put forward by Rep. Rush Holt, D-N.J., is still in committee. It has 143 co-sponsors.

"It's not a partisan issue," said Patrick Eddington, Holt's communications director. "To us, it's just a common sense way to safeguard elections and individual votes."

Pennsylvania is one of 12 states in which legislators have not proposed paper requirements.

"We'd like to see that change," said Pamela Smith, of California-based Verified Voting, founded by David Dill, a professor of computer science at Stanford University. "Machines do malfunction. When that happens, voters are disenfranchised."

Smith thinks states should take advantage of the millions of dollars in federal money available now to make sure they have paper trails for their machines. Ideally, she said, voting precincts would forgo the flashier touch-screen systems and use optical scanners that read fill-in-the-bubble paper sheets, similar to those used for standardized tests. That way, even if the scanners malfunction, voters can still cast their ballots.

"Paper doesn't fail to boot up," Smith said.

Still, paper for optical scanners is expensive, said Regis Young, Butler County's elections director. Programming a touch-screen machine is easier and cheaper than printing tens of thousands of ballots.

Many computerized machines can be equipped with a printer that enables voters to view a paper copy of their choices through a glass case. Because of confidentiality concerns, voters can't take a receipt from a polling precinct with them.

But, unless there is a state or federal requirement, Young doesn't think Butler County will buy the printers. The county currently uses punch cards at its 82 precincts and could receive as much as $954,000 in federal money for new equipment.

Shamos doesn't see a need for paper trails and says the state's rigorous testing should identify problematic machines.

"A badly designed system might be vulnerable, and that's what we look for," he said.

Despite such reassurances, local officials are hoping to become more involved in the process. Allegheny County Councilman Dave Fawcett, a member of the county elections board, said he hoped to organize a public meeting about new machines.

The story of UniLect Co., a company based in the San Francisco Bay area, illustrates some of the potential pitfalls of computer voting.

After the 2000 election, the company's Patriot touch-screen system became hugely popular nationwide. In 2001, Mercer County spent $900,000 for the system. Beaver and Greene counties had purchased the system several years earlier.

For the most part, UniLect's machines performed well. In November, however, one machine in North Carolina lost almost 4,500 votes, throwing doubt over a close race for the state's agriculture commissioner. Mercer County also saw a 7 percent presidential undervote.

UniLect officials defended the machines, blaming the mistakes on errors made at the local level. In Carteret County, N.C., the machine issued an alert -- "voter log full" -- after the first 3,500 votes. But unaware voters kept casting votes, and no precinct workers noticed the alert.

"The machines did not fail. They were only doing what the program was telling them to do," said Andrew Burkhart, director of operations at UniLect. He said local officials could have programmed the machine to take up to 10,000 votes.

But computer experts, including Shamos, argued that the machine should not have kept accepting votes once it was full. Earlier this month, the Carteret Board of Elections decided to get rid of their UniLect machines.

In Mercer County, election officials made programming errors, resulting in the resignation of Election Director James Bennington.

A group of voters from Beaver County petitioned the state to test the Patriot. Shamos conducted the tests. He found several problems, including a way to change vote totals on the machine.

In April, the state decertified the Patriot, forcing Mercer, Beaver and Greene counties to print paper ballots for the May 17 primary election.

UniLect officials have asked for a new round of tests. One had been scheduled for Friday, but it was postponed. Now, Shamos says, the company is accusing the professor of bias and wants the state to replace him. But he stands by his work.

"All you get from UniLect is excuses," he said.

Greene County Elections Director Frances Pratt said she never had serious problems with the UniLect system, which the county bought in 1998 for $350,000. Now, the county may have to buy new machines.

"We are waiting to see the outcome of the re-examination before we decide anything," Pratt said.

She said county election directors throughout the state will have a chance to see new machines at a conference in Philadelphia next month. Yet they are still months away from making purchases.

"It's a huge undertaking," Westmoreland County Elections Director Paula Pedicone said. "It's going to have to be done with a lot of care."