SAN FRANCISCO – A majority of California voters oppose a November ballot initiative that would amend the state constitution to ban same-sex marriage, according to a survey released Friday.

The Field Poll found that 51 percent of likely voters say they would vote against Proposition 8, while 42 percent say they would vote for it.

The poll shows a turnaround from 2000, when 61 percent of voters cast ballots in favor Proposition 22, which strengthened the state's 1978 one-man, one-woman marriage law with the words “Only marriage between a man and a woman is valid or recognized in California.”

That vote came a year after the state Legislature enacted the first of a series of laws awarding spousal rights to domestic partners.

This year's ballot initiative comes on the heels of a landmark California Supreme Court decision in May that granted marriage rights to same-sex couples.

Hundreds of gay and lesbian couples have flooded county clerk's offices throughout the state to receive marriage licenses since the ruling took effect in June.

The poll found that Democrats and Republican voters were starkly divided on the issue. Sixty-three percent of Democrats said they would vote against the measure, while 68 percent of Republicans said they would vote for it. Nonpartisans were against the initiative 66 percent to 27 percent.

The poll found the greatest opposition to the ballot measure among voters living in California's coastal counties and large cities, as well as among voters younger than 30. In the San Francisco Bay area, 67 percent of voters oppose Proposition 8, while only 26 percent approve.

The Field Research Corp. surveyed a random sample of 672 likely voters during the week of July 8-14.