WASHINGTON--Eight years after glitches marred the 2000 presidential elections, Americans are still struggling over voting machine technology amid growing concerns about the reliability of electronic systems.

Many jurisdictions are reconsidering new technology and moving away from paperless and touch-screen voting machines -- systems which had been seen as a cure for the problems of punch cards that notably failed to correctly tally votes in 2000 in Florida.

A growing movement of activists, including many computer scientists, are leading calls to shift away from paperless systems, saying they are vulnerable to software and hardware glitches or manipulation by hackers or others.

About 80 percent of Americans use systems where votes are cast or tabulated by computer including 38 percent who used so-called direct recording electronic voting machines (DRE), according to a study by John McCormally of the University of Iowa.

Many of the DREs have no "paper trail," which according to critics makes a recount or audit impossible.

Alan Dechert, a computer scientist who heads the activist Open Voting Consortium, said paperless touch-screen voting systems have failed in many cases, causing these systems to be tossed out of many states and localities.

With paperless systems, Dechert said, "you can't have a recount because there is nothing to recount."

Dechert's group and others opposed to paperless votes point to dozens of instances in which machines have failed, or results were questionable because of undercounted or irregular patterns in voting.

"It doesn't matter if it's a crooked system or if it is an accident. When you have close elections this becomes an instance whether the outcome can be decided by lawyers and judges instead of voters," Dechert said.

Voting machine manufacturers argue they are reliable. And a Government Accountability Office report said there was no evidence that electronic machines were the source of a large "undervote" in a 2006 congressional election in Sarasota, Florida, cited by many critics of paperless voting.

Warren Stewart, project director at the activist Verified Voting Foundation, said growing doubts about the reliability of paperless systems leaves the 2008 presidential election open to another potential calamity.

"It's highly probable we could have a situation where the results come down to one state, and we have a situation where we can't resolve it" because of an inability to recount electronic vote tallies, he said.

Stewart cited "a fundamental problem with counting votes in the computer memory."

"Whether it's an error or malicious attack, there's no safety net," he said.

Stewart said the most reliable systems appear to be so-called optical scan devices in which voters mark their choice on paper ballots which are read by computerized scanners.

Dechert meanwhile argues that touch-screen systems can be accurate if backed by a paper printout which becomes the actual ballot. He also argues for "open source" machines in which software can be verified by outside experts.

A study by the Pew Center on the States noted five states that had revamped their voting systems after 2000 are now in the process of a second overhaul because of discontent over electronic machines.

California banned a large number of touch-screen voting devices after a review concluded that DRE machines "were inadequate to ensure accuracy and integrity of the election results," according to California Secretary of State Debra Bowen.

A study in Ohio found "electronic voting systems have critical security failures which could impact the integrity of elections," according to that state's top election official.

Similar reviews are underway in Florida and Colorado and New Mexico, with other states also hesitating.

A study by David Kimball of the University of Missouri found that error rates for touch-screen machines in 2004 were just 1.0 percent for newer models and 1.2 percent for older models.

That was close to the average 1.1-percent estimated error rate nationally and better than the 1.8 percent for punch cards -- the devices that produced the "hanging chads" in Florida in the contested 2000 race.

Richard Soudriette, president emeritus of the International Foundation for Election Systems (IFES), says touch-screen electronic machines have been "unfairly maligned."

Soudriette said these systems are gaining acceptance in other countries, notably Brazil and India. But in the US, a hodgepodge of state, federal and local regulations make it difficult to set standards, he said.

"I think all election officials in the US need to get together and work out a protocol on how systems will be certified and get everybody fully onboard," he said.

"If I was an election administrator and it was my job, I would probably go with a paper-based system, because people feel more comfortable with that. But it would be irresponsible to take equipment purchased over the last couple of years and junk it because it doesn't fit people's impression of what is the best technology."