When some 200,000 voters in Riverside County go to the polls Tuesday, they'll cast votes on a computerized voting system that is subject to an ever-larger number of safeguards, but that continues to generate controversy and demands for additional security.

Riverside County used touch-screen voting terminals in a San Jacinto municipal election in August 1999, and became the first county in California to do so on a large scale that November. By the 2000 presidential election, every polling place in the county was equipped with them.

The chaos that paper ballots created elsewhere that year -- most notably in Florida -- hastened the adoption of touchscreens around the country, but it also showed Americans how flaws in voting systems could leave even the results of a presidential election in question.

Since then, more and more U.S. cities and counties have begun using touchscreens. By November 2004, about 50 million -- or 29 percent -- of the nation's voters were registered in counties that use touchscreens, according to Election Data Services Inc., a consulting firm. Recent studies have estimated that another 10 million to 20 million U.S. voters will use touch screens for the first time Tuesday.

At the same time, voters' distrust of them remains surprisingly strong. Several states and counties have abandoned touchscreens in the last two years.

About 80 percent of Americans believe that election officials shouldn't rely solely on the machines and their proprietary software, according to a poll of 1,018 adults conducted in August by Zogby International.

In a Gallup survey of 526 likely voters last month, 46 percent of registered voters expressed a "great deal" of confidence in electronic voting machines, with 34 percent expressing a "fair amount" and 19 percent expressing "not much." Paper ballots fared slightly worse, with 38 percent of voters expressing "great confidence" and 22 percent expressing "not much."

The distrust has been fueled by people ranging from conspiracy theorists to voters who have experienced actual glitches with the machines. Additionally, several computer scientists have demonstrated how -- in the absence of thorough oversight -- the computers can be hacked and vote tallies changed on a large scale, though no such hacking attempt has been documented in an actual election.

In California, new regulations have aimed to boost confidence and provide reliable backup to the electronic machines. This year's primary elections, in June, were the first to require a paper printout of each vote cast on the electronic machines. Such printouts stay inside the machines and are fished out in the event of a recount.

A random 1 percent of those printouts are counted in every race as a check of the reliability of the electronic tally. A similar requirement has existed for 40 years, but it was just last year that the state Legislature applied it explicitly to touch-screen systems.

"We've made a huge amount of progress in California over the last six years," said Kim Alexander, president of the nonprofit California Voter Foundation. "But we still have a long way to go."

The entire nation is a patchwork of voting systems. In several states, such as Georgia and Nevada, every county uses touch screens.

Alabama, Michigan and several other states don't allow them. In Oregon, a voter marks and then mails in a paper ballot or hand-delivers it to the local county elections office.

Many other states are themselves patchworks of voting systems. California's secretary of state has certified a range of voting machines. Most counties use touchscreens made by Sequoia Voting Systems of Oakland, as Riverside County does; by Ohio-based Diebold Inc., which San Diego County uses; or by Election Systems & Software of Omaha.

Some of the same counties -- and others -- use what are known as "optical scan" ballots. Voters indicate their choices by filling in circles or squares on the ballots; an electronic machine scans and counts them.

California's voting systems, as a whole, compare favorably to most other states' in terms of security and ease of use, Alexander said. Still, she bemoaned the wide variations among the counties, saying that too many have low security standards or don't make voting as easy as they could.

One example of that variety is in the practice of posting the vote counts from each precinct at the polling place. The California Elections Code appears to require the practice, which goes back at least to the 1960s, but elections officials in more than half of the counties in the state have given it up, saying the requirement applied only to machines in use in the 1960s.

Such posting is intended to allow citizen watchdog groups to doublecheck the tallies generated by machines at the precinct against the tallies produced by a central counter.

Following demands from a group of activists, Riverside County Registrar of Voters Barbara Dunmore said last month that poll workers at about three-quarters of the county's 600 polling places would have to post their vote tallies. For security and privacy reasons, polls at schools and private residences would be exempt.

Tom Courbat, a Murrieta resident who is leading the group in a poll-monitoring project, praised that move and several others Dunmore has made this year. For both the June and November elections, Dunmore convened a semi-official Election Observer Panel representing political parties and community groups, as state election code requires.

"We believe they would not have happened if we had not been in the forefront and pushed," Courbat said.

Still, Courbat and members of his group, Democracy for America-Temecula Valley, have complained that Dunmore has responded too slowly or not at all to other demands for more public oversight. The group members have recently addressed several Board of Supervisors meetings during periods for open public comment, leading to testy exchanges with supervisors and the county's chief executive officer, Larry Parrish. Third District Supervisor Jeff Stone called the group a "mockery of democracy" at a board meeting last month.

"You won't be happy until you can substitute your judgment for Barbara Dunmore's and everybody else's," Parrish told Courbat at the board's meeting Tuesday.

One issue at hand that day was another state law dating from the days of paper ballots, a requirement that citizens be able to watch the counting process. Riverside County elections officials have allowed observers to view employees as they operate the computer that tallies the votes, but Courbat and his group have protested that observers aren't allowed close enough to read the computer monitors.

Nonetheless, Alexander said, Riverside and most other counties have demanded higher standards for voting systems' security and usability than most other states.

Under Secretary of State Bruce McPherson, for example, California became one of the first states in the nation to require extensive testing of new voting machines under conditions similar to what they face in real elections, Alexander said.

The requirements that touch-screen systems produce paper records -- and that voters be able to check them before leaving the booth -- were also among the first in the nation, when ordered by McPherson's predecessor in 2003 and codified in 2004 by bipartisan legislation.

The bill requiring those paper records to be used to check the machines' accuracy, too, was one of the first such bills in the nation.

Debra Bowen, D-Redondo Beach, has led the state Senate's elections committee, authoring that bill and a dozen others. She is challenging McPherson in his bid for re-election.

In their final days of campaigning, the two candidates have touted their records of helping to secure elections. McPherson appeared in San Diego on Tuesday to express confidence in electronic voting machines, which voters there will use this week for the first time since 2004. He was scheduled to make a similar appearance in Riverside and Ontario today.

Bowen, for her part, has sent out several recent press releases, criticizing what she calls McPherson's failure to protect the state's voting systems sufficiently from fraud. On its Web site, her campaign has posted a "10-point plan to restore confidence in California's voting system."

Contact staff writer Chris Bagley at (951) 676-4315, Ext. 2615, or cbagley@californian.com.