Gay rights activists and a legal scholar said Friday's ruling could provide ammunition for overturning Proposition 8, either in court or at the ballot box. During a hearing last month, a majority of the California court appeared ready to uphold the ballot measure.

In the Iowa decision, Justice Mark Cady wrote: "We are firmly convinced the exclusion of gay and lesbian people from the institution of civil marriage does not substantially further any important governmental objective. The Legislature has excluded a historically disfavored class of persons from a supremely important civil institution without a constitutionally sufficient justification."

Gay rights advocates were jubilant.

"It's a red-letter day for us here in Iowa," said Matt McCoy, a gay member of the state Senate who cheered the decision from the courthouse steps in Des Moines.