Louisiana voters overwhelmingly approved a state constitutional amendment banning same-sex marriages and civil unions, one of as many as 12 such measures on state ballots this year.

With 80 percent of the precincts reporting, the amendment was winning approval, with 79 percent of the vote. Only in New Orleans, home to a politically strong gay community, did the race appear to be close; incomplete returns there showed slightly more voters opposing the measure than approving it.

Christian conservatives had conducted an intense grass-roots lobbying campaign for the amendment. Gene Mills of the Louisiana Family Forum outlined a statewide effort relying on word of mouth, meetings with pastors and some advertising.

The civil rights group Forum for Equality promised a legal challenge to the ban. A first round of court fights was turned away by state courts, saying that an election cannot be challenged until the vote is taken.

Forum for Equality attorney John Rawls said there are many possible grounds for challenging the results in state and federal court. One appeared Saturday, when voting machines were delivered late to some New Orleans precincts, keeping some people from casting ballots for hours. State director of elections Frances Sims said at least 59 precincts did not have voting machines when polls opened because officials with the New Orleans clerk of court's office failed to meet drivers who tried to deliver the machines earlier that morning. The problem was solved by midday.

Julius Green, 58, said he went to his polling place in New Orleans's Bywater neighborhood about 10 a.m. and found no voting machines -- just a crowd. "I am angry. I'm very angry," Green said.

Louisiana already has a law stating that marriage can only be between a man and woman, but supporters of the amendment want to protect that restriction in the state constitution. The amendment would also prohibit state officials and courts from recognizing out-of-state marriages and civil unions between homosexuals.