LOS ANGELES — For the third time in four years, California voters are deciding whether doctors should be required to notify parents before performing an abortion on an unemancipated minor.

Proposition 4, similar to laws in 35 states, also requires a 48-hour waiting period.

In 2005, the first year the abortion question was on the ballot, 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 are hoping the election will bring enough of their supporters to finally put the measure over the top. Proposition 8, which would constitutionally ban same-sex marriage, also is expected to bring social conservatives to the polls in large numbers.

Proponents of the abortion-notification initiative say minor language tweaks in their latest attempt should make the measure more palatable to voters. The changes are intended to answer arguments that some minors could be abused if their parents were told of their pregnancies.

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

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

They say the provision for minors who do not want their parents told 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 say, would not want to disclose abuse if they knew it would lead to an investigation.

Proposition 4’s principal sponsor is James Holman, publisher of the San Diego Reader, a weekly newspaper. He has 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 supports Proposition 4, while the California Teachers Association opposes it.

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