9:45 p.m.LOS ANGELES — For the third time in four years, California voters weighed whether doctors should be required to notify parents before performing an abortion on a minor.

In early returns, the ballot measure appeared to be splitting the vote.

Similar to laws in 35 states, Proposition 4 also requires a two-day waiting period. Voters have twice defeated very similar measures in 2005 and 2006. In 2005, 54 percent voted against it. A year later, that rose to 56 percent.

But with a presidential election bringing out many more voters than usual, proponents hoped the election would bring enough of their supporters to finally pass the measure. Another ballot initiative to constitutionally ban same-sex marriage was expected to bring social conservatives to the polls in large numbers.

Ballot measures to limit or ban abortion were 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. It didn’t explicitly mention abortion, but activists on both sides in the campaign viewed it 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 were 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 said minor language tweaks in their latest attempt would make it more palatable to voters. The changes were intended to answer arguments that some unemancipated minors could be abused if their parents were told of their pregnancies.

The latest version would allow minors to request that another adult relative, instead of a parent or guardian, be notified.

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

They claimed the provision for minors who do not want their parents notified requires that the minor write a detailed statement that the health care provider must report, triggering an investigation by Child Protection Services. Many teenagers, the opponents said, would not want to disclose abuse if they knew it would lead to an investigation.

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.

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

The principal opponents include several chapters of Planned Parenthood, which helped the No on 4 campaign raise $6.4 million.