1:30 p.m.LOS ANGELES — A ballot measure that would require doctors to notify parents before performing an abortion on a minor was rejected by voters, but supporters vowed Wednesday to put the issue on the ballot a fourth time.

With almost all precincts reporting, 52.1 percent of voters were opposed to Proposition 4 while 47.9 percent favored it.

Similar to laws in 35 states, the ballot initiative would also have required a two-day waiting period before minors could get abortions.

Voters twice defeated similar measures in 2005 and 2006, but with a historic presidential election inspiring huge voter turnouts, proponents hoped the election would bring enough of their supporters to finally pass the measure. A ballot initiative that succeeded in banning same-sex marriage was also expected to draw social conservatives to the polls.

Proponents of the measure conceded defeat and said it was a “grave injustice” to teenage girls, and vowed to continue to try to get the measure passed by voters.

“I think many Californians are going to be disappointed,” said Paul Laubacher, a spokesman for the Yes on 4 campaign. “What was Obama’s comment? ’Yes we can?’ I think that’s appropriate for our cause.”

Kathy Kneer, president of Planned Parenthood Affiliates of California, which funded and organized opposition to the measure, said the vote sent a clear message that voters here did not believe the measure was designed for the safety of young women.

“The proponents tried to deceive the voters,” Kneer said.

Ballot measures to limit or ban abortion were also defeated in two other states. In South Dakota, voters rejected an initiative that would ban abortion except in cases of rape, incest and serious health threat to the mother. In Colorado, voters defeated a measure that would have rewritten the constitution to define human life as beginning at conception, which both sides in the campaign viewed as a direct challenge to abortion rights.

In California, young and older voters appeared split on Proposition 4, with preliminary exit polls showing voters under 30 heavily opposed to it, while voters 65 and over supported it. Age groups in between were more evenly split.

Proponents of the abortion-notification initiative hoped minor language tweaks in their latest attempt would make it more palatable to voters. The changes were intended to answer arguments that some girls might be abused if their parents learned they were pregnant.

The latest version would allow minors to notify another adult relative, instead of a parent or guardian.

Opponents said Proposition 4 was a thinly disguised attempt to chip away at abortion rights.

Under a provision of the measure, girls who feared they would be abused if they told their parents they were pregnant would have to give a detailed statement to health care providers that would result in an investigation by authorities. Opponents said many teenagers would not want to disclose abuse if they knew it would lead to such a probe.

Proposition 4’s principal sponsor was James Holman, publisher of the San Diego Reader, a weekly newspaper. He contributed more than $1.3 million of the reported $2.6 million raised for the measure. He also bankrolled the 2005 and 2006 measures.

The No on 4 campaign, largely funded by Planned Parenthood Affiliates of California, raised $8.2 million.

Gov. Arnold Schwarzenegger supported Proposition 4, while the California Teachers Association opposed it.