WASHINGTON -- You can try to vote for George Washington, but Benedict Arnold will win.

At least that's the scenario on a Diebold touch-screen voting machine toted around Capitol Hill yesterday by Edward W. Felten, a professor of computer science and public affairs at Princeton University.

He hoped to persuade lawmakers that a new generation of voting technology being deployed across the country still faces worrisome security flaws and should have paper trails that voters can check.

"There's really no limit to the amount of mischief that can be done," he said.

In a packed hearing room, the professor demonstrated how to implant a virus on a Diebold AccuVote-TS and distort the results of a mock election between America's most revered founding father and its most infamous traitor. He said he bought keys to open the unit on the Internet. The virus could, theoretically, infect portable memory cards and transfer itself to other machines, possibly upsetting thousands of votes.

A newer version of the Diebold machine is being used by 16 Pennsylvania counties, including Armstrong, Clarion, Somerset, Warren and Washington.

State officials had been aware of the AccuVote's flaws and have advised counties to take cautionary measures, according to Michael Shamos, a Carnegie Mellon University computer science professor who tests voting machines for the state.

David Bear, a spokesman for Diebold, said the AccuVote is only vulnerable if a computer expert obtains unfettered access.

"That's not reflective of a real election environment," he said.

Washington County Elections Director Larry Spahr agreed, saying his office guards voting equipment closely.

Still, the possibility of a major security breach worries Mr. Felten, and his testimony comes on the heels of high-profile malfunctions in several primary elections this year, including problems that delayed voting at precincts in Maryland two weeks ago.

Local governments nationwide have been upgrading their voting technology to satisfy the Help America Vote Act, or HAVA, a law passed by Congress in the wake of the notorious hanging chads of the 2000 presidential election in Florida.

In May, Allegheny County used the ES&S iVotronic, a touch-screen machine, for the first time, encountering only minor glitches.

Mr. Felten yesterday voiced strong support for an extension of HAVA that would require the use of machines with paper trails and a routine audit of those trails. The bill, proposed by Rep. Rush Holt, D-N.J., has 215 co-sponsors, but it likely won't come up for a vote this year. It also has the backing of the League of Women Voters and the Association for Computing Machinery.

Twenty-eight states already have requirements that mirror the Holt bill, and Pennsylvania legislators are considering similar requirements.

But Mr. Shamos, who also was in Washington, D.C., yesterday to testify before the House Administration Committee, warned that a new federal law could make many new machines obsolete, wasting billions of dollars in federal aid that counties have already spent on upgrades.

He argued that paper often is prone to errors of its own. He cited problems in the May primary election in Cuyahoga County, Ohio, where paper printers attached to touch-screen machines produced illegible or blank rolls, affecting as much as 10 percent of the county's backup paper records.

Another paper alternative is the optical scan ballot, which resembles a fill-in-the-bubble standardized test. Those ballots, too, could be lost or altered, Mr. Shamos said.

Mr. Felten's concerns about the Diebold machine, he said, are legitimate.

"Some of these vulnerabilities are severe, and require immediate repair. But the point is that they are also easily remedied," he said.

"When tainted spinach was found in California, Congress did not ban the eating or distribution of leafy vegetables, even though at least one human life had been lost. The appropriate reaction to the discovery of a security flaw is to repair it."

In the meantime, computer scientists must develop more reliable ways of verifying electronic votes, Mr. Shamos said.

Mr. Spahr said voters in Washington County were satisfied with their first trials of almost 700 Diebold voting machines in May, and he stressed the importance of security in training sessions with poll workers.

Allegheny County locks up its 4,600 iVotronic machines in a warehouse on the North Side. Next week, the county will begin a new round of training sessions for as many as 6,500 poll workers. Those sessions will emphasize issues that led to problems in May, including how to open a polling site using the new machines.

Kevin Evanto, a spokesman for county Chief Executive Dan Onorato, said the county has already negotiated a deal with ES&S to add a paper trail component to each machine if the state or federal government mandates such a change.

"Allegheny County is ready to go whenever we can," he said.