SAN FRANCISCO - The California Supreme Court ruling legalizing gay marriage will not be the last word. California voters will almost certainly hold a referendum on a constitutional amendment banning same-sex marriage in November, and for the first time anywhere in the U.S., the vote will have a direct and immediate effect on gay couples waiting to tie the knot. The amendment needs a simple majority to pass, and if the voters reject gay marriage, their decision will supersede the high court’s. There are signs the contest’s outcome will be close.