Gay marriage supporters are particularly interested in the Iowa Supreme Court's ruling, which they hope will sway the California Supreme Court to overturn the ballot measure voters passed with 52 percent of the vote in November.

But opponents say the Iowa decision should have no bearing on the essential issue before the high court: Whether voters have the right to amend California's constitution at the polls.

California's Proposition 8, similar to laws in 29 other states that ban gay marriage, was the most expensive ballot measure in the nation, with $83 million poured into campaigns on either side.

The measure was introduced largely as a reaction to the California Supreme Court's decision in May to legalize same-sex unions. That ruling was extensively cited by Iowa justices in their decision released Friday.

California's highly anticipated ruling on Proposition 8 could come any time before June 3. Some 18,000 gay and lesbian couples were wed in the 4 1/2 months it was legal to do so in California.

Shannon Minter, legal director of the National Center for Lesbian Rights, who led the challenge to Proposition 8 in oral arguments before the California court last month, was jubilant Tuesday after Vermont joined Massachusetts, Connecticut and Iowa as the fourth state to allow gay marriage.