A growing movement in favor of instant-runoff voting in Alameda County is being thwarted by the manufacturer of the county's electronic voting machines, critics charged Tuesday.

At a rally at the county administration building, protesters chided Diebold Elections Systems, and recent assertions that it will cost up to $2 million and take at least a year for software upgrades and other work needed to allow Alameda County's Diebold voting machines to tabulate instant runoffs.

Critics said the revelations clash with promises made by the manufacturer at the time Alameda County purchased the electronic machines for $12 million in 2002.

They brandished copies of bid documents issued before the purchase, claiming the machines "can easily be programmed" to conduct instant runoffs.

"Presumably they said that because they wanted to get the contract," said Kriss Worthington, a city councilman in Berkeley, where voters last year authorized instant runoffs.

Referring to Texas-based Diebold, Worthington added: "But now that we have several cities pushing for instant-runoff voting, they're singing a different tune."

Instant runoffs allow voters to rank their choices for elective office as a way to decide races involving the two top vote-getters without having to conduct costly special runoff elections. If either of the top finishers fails to achieve a majority vote, an "instant runoff" is conducted by counting voters' second- and third-ranked choices.

The concept has gained popularity in recent years as the need for special elections has grown more frequent and costs have increased.

With cost estimates emerging three years after the county was promised equipment that could easily be modified, "many feel Diebold is being disingenuous with us," said Rodney Brooks, chief of staff to county Supervisor Keith Carson.

Dielbold spokesman David Bear said Tuesday that he was unaware of the $2 million price tag attached to the upgrades needed in Alameda County, but agreed that software enhancements and other work would "carry some costs."

"We continue to work in partnership with Alameda County,"" Bear said. "But people need to understand that (the required upgrades) can't just happen over night."

The $2 million cost cited by protesters came from a March letter by Bradley Clark, Alameda County's registrar of voters, who wrote to the county's Council of Leagues of Women Voters that "costs associated with development of software to conduct an Instant Runoff Election could be up to $2 million."

Clark last week accepted a job with the California Secretary of State's office, and is working in his Alameda County post only two days a week as he prepares for the transition. He could not be reached for comment Tuesday.