Berkeley voters appeared to be decisively approving a ballot measure that would have the city pursue instant-runoff elections, a system that has yet to be tried in California.

The vote on Measure I was largely symbolic. Alameda County elections officials have said they will not allow instant runoffs, in which voters rank candidates by preference, until the state adopts guidelines for such elections.

With nearly half of precincts counted Tuesday, Berkeley voters Tuesday also were approving Measure H, which would require that a traditional runoff be held only if the leading candidate fails to win 40 percent of the vote in a general election.

The threshold is now 45 percent. The City Council unanimously put Measure H before voters in hopes of avoiding some runoff elections. The measure would be superseded if instant-runoff elections became a reality.

The council voted 6-3 to put Measure I before voters. City officials have not decided how an instant-runoff system would work, other than that it would be used in elections for mayor, City Council and auditor, and that it would take effect only if it doesn't increase the cost of elections.

The city of Cambridge, Mass., has used a form of instant-runoff voting to select its City Council for decades. In 2002, San Francisco became the first California city to approve instant runoffs. Despite spending $1.6 million in technology upgrades, however, the process has been held up by obstacles that include the city's failure to win the state's go-ahead. City officials say a system will be in place for the November election.

In San Francisco, voters will rank candidates using an electronic voting system. The last-place vote-getter will be thrown out after the first round, and his or her votes will go to the voter's second choice. The process will continue until someone has a majority.

Supporters in Berkeley say such a system would cut costs by eliminating traditional runoffs and would also increase voter interest. Opponents say it is unproven and would confuse voters.

The League of Women Voters, which is leading a national push for instant runoffs, hopes that if enough California cities pass such measures, the state will adopt standards for the new voting system.

Supporters of Berkeley's Measure I say instant-runoff voting would draw candidates from outside the mainstream, save money and reduce negative campaigning by forcing candidates to appeal to a broader base.

Berkeley spent $90,000 on a December 2002 runoff for a City Council seat, said City Clerk Sherry Kelly. In 1998, the city spent $100,000 preparing for a runoff that wasn't needed, she said.

But opponents say instant-runoff balloting -- particularly if combined with countywide or statewide races in which the traditional method is used -- would lead to confusion and spoiled ballots. They also noted that Berkeley's measure did not specify how votes would be counted, a potential problem highlighted by last year's recall of former Gov. Gray Davis and a list of 133 replacement candidates.