Frustrated by the cost of multiple elections to fill council seats and the difficulty of limiting the influence of special interests, San Jose officials Thursday took a hard look at wholesale change in the way voters choose their city leaders.

City leaders are considering joining San Francisco in using "instant-runoff voting," which lets voters rank their first, second and third choices among a field of candidates. If no candidate receives more than half of the first-choice votes, the second and, if necessary, third choice votes are applied immediately until one candidate garners a majority. That avoids making the top two finishers compete again in a runoff election.

Advocates say the system is less costly to taxpayers, noting the $250,000 to $500,000 expense of each election in San Jose. It's also cheaper for council candidates, who typically spend $90,000 to $100,000 for an election, often raised from deep-pocketed interests with expectations that their donations will buy support.

Backers also say the system boosts voter participation by reducing the nasty mudslinging many voters find off-putting in longer campaigns.

"I think it's the right choice for us," said Councilman Sam Liccardo at a Thursday forum sponsored by the New America Foundation and Common Cause. "The question is how we get there."

San Jose officials have been toying with the idea for a few years. Mayor Chuck Reed expressed interest in instant runoffs during the 2006 campaign. The city's elections commission has been studying instant-runoff voting and will consider it again at its meeting next month.

But amid the city's multimillion dollar deficits, the hang-up has been the six-figure cost of putting a charter amendment on the ballot, since voter approval is needed to change the system.

Sponsors of Thursday's forum at the city's main library noted that elections officials, campaign consultants and some political interests have aired concerns about instant runoffs. The added complexity is a hassle for elections officials; shorter election cycles provide less business for campaign consultants; and some political groups fear the system will help marginal candidates with little mainstream support pull off surprise victories.

Skeptics also say a runoff campaign gives voters a deeper look at the top two candidates, allowing more time to air dirty laundry and expose fatal flaws before it's too late. Those opponents have pointed to the case of Ed Jew, a San Francisco florist elected through that city's instant runoff system to the Board of Supervisors in 2006, only to be ousted within a year after it was found he actually lived in Burlingame.

But instant-runoff defenders noted that the current system has produced some deeply flawed candidates in San Jose, such as Terry Gregory, a former District 7 councilman who resigned over illegal gifts in 2005.

Liccardo said he likes the idea because he found that while visiting the same voters a second time in his runoff election, he had little new to say to them, and yet it doubled his cost to run for office. Councilman Ash Kalra, who also participated in Thursday's forum, called the idea worth considering, citing his odd journey to office last year against a candidate who withdrew too late to pull her name from the ballot. The city's rules required a runoff even though his opponent was no longer in the race.

Santa Clara County elections officials and the California Association of Clerks and Elections Officials have no official position on instant runoffs. San Francisco has been using the system since 2004, and it has been used in other states such as Vermont, Maryland and North Carolina and in countries including Australia and Ireland.

Oakland, Berkeley and San Leandro are expected to begin using it next year, and it is also being studied in Los Angeles, Long Beach and Pasadena.

San Jose Democratic strategist Jude Barry said "the jury's still out" on instant-runoff voting, but he said voters should be wary of the reliability of the technology calculating the ranked choices.

"I'd be concerned about making the system more complicated and maintaining public confidence in the accuracy of the outcome," Barry said.

But Jay Rosenthal, a San Francisco-based political consultant who advised Liccardo's 2006 campaigns and has voted in San Francisco's instant runoff elections, said he's not worried about such a system depriving him of business. Few consultants, he said, rely on multiple municipal elections to make a living.

"I was skeptical at first. A lot of people were," Rosenthal said. "But it's not as complex as people thought it would be. And the people who would have won the traditional way won in the instant runoff."