But in Silicon Valley, computer scientists are calling for a halt to the trend - at least until voting machines are redesigned to produce a paper record of every vote.
The idea is to provide more protection against hackers - or political hacks - who might tamper with the results.
A test case in Santa Clara County ended in disappointment Tuesday for proponents of paper records. The local board of supervisors had the chance to make Santa Clara the nation's first county to purchase the so-called voter-verified paper backup system, but it voted instead to invest $20 million in 5,000 touch-screen machines that won't produce paper receipts.
"I'm disappointed," said Peter G. Neumann, principal scientist at the computer science lab at Menlo Park-based SRI International. "You'd think we'd have enough of an understanding of computers to know that a voter-verified paper backup system is the absolute only way you can have any integrity whatsoever in elections."
Putting faith in systems that create no records outside cyberspace could open to the door to election fraud of unprecedented proportions, some experts say.
"Every election system we've ever created has had someone rig it, but it's been only on a local basis," said Bev Harris, author of "Black Box Voting: Ballot-Tampering in the 21st Century. "Now it only takes one programmer to insert malicious code into a computer system that runs election machines all over the country."
Congress has set aside $3.9 billion for states to overhaul their voting systems, and elections experts say as many as 75 percent of voters nationwide will cast ballots electronically by 2010.
Harris and other voter-rights advocates worry about the concentration of power in the four companies that dominate the market for electronic voting machines: Election Systems & Software, Sequoia Voting Systems, Diebold Election Systems and Hart
Advocates worry that a software developer could insert a back door into the code, allowing someone to hack in and change results.
Scientists also worry that paperless machines, like all computers, could fall victim to server crashes, power outages, frozen screens, software bugs and other glitches.
"Even my ATM has the courtesy of asking if I want a receipt," said Kim Alexander, president of the Sacramento-based nonprofit California Voter Foundation. "My pay-at-the-pump Visa transaction is more secure than my voting ballot if my county goes to paperless voting."
The companies that make electronic voting machines say the security concerns are overblown, noting that they must meet standards set by the Federal Election Commission and the National Association of State Election Directors.
And some see the paper trail as a waste of money and another layer of complexity at a time when state and local governments face their worst budget shortfalls in years.
In response to the concerns in Santa Clara, Oakland-based Sequoia built prototypes that produce paper receipts. Sequoia has offered to add the printers without raising the price of Santa Clara County's $20 million contract.
But company spokeswoman Kathryn Ferguson warned of other problems.
"You'll have printer jams, you'll run out of paper, you'll have voters say, `That's not how I voted,' and you'll have to have procedures for letting them re-vote and to determine which of the receipts you printed was the valid one, and which of those constitute the official recount in case of a contested vote," said Ferguson, a former voting administrator in three states. "It would create a lot more problems than it solves."
By Rachel Konrad