Gay marriage was put to a vote in Maine on Tuesday in a closely watched referendum that gay-rights activists across the country hoped would prove for the first time that their cause can prevail at the ballot box. Voters had to decide whether to repeal or affirm a state law that would allow gay couples to wed. The law was passed by the Legislature in May but never took effect because of a petition drive by conservatives. Early returns showed a close contest, as forecast. With 229 of 608 precincts reporting, each side had 50 percent. A vote to uphold the law would mark the first time that the electorate in any state endorsed gay marriage. That could energize activists nationwide and blunt conservative claims that same-sex marriage is being...