* Ruling expected in weeks
* District court ruling sure to be appealed
* Judge asks if gays deserve special protection
* If Supreme Court takes case, could be landmark (Adds closing from Prop 8 lawyer, judge questions)
By Peter Henderson
SAN FRANCISCO, June 16 (Reuters) - A six-month trial on whether to overturn a California ban on gay marriage ended dramatically on Wednesday when a lawyer defending the prohibition said he did not need evidence to prove the purpose of marriage.
The case is likely headed for the U.S. Supreme Court no matter how District Court Chief Judge Vaughn Walker rules on California's gay marriage ban. A decision there could determine the fate of same-sex marriage in the United States for years.
California voters approved the ban known as Prop 8 in 2008, dismaying gay advocates and their allies who had hoped the trend-setting state would side with them.
However U.S. voters in state referendums across the nation have consistently opposed same-sex marriage. It is legal in only five states and the District of Columbia due to court and legislative action.
Arguing for the ban to be reversed was conservative jurist Ted Olson, who served as U.S. solicitor general under former President George W. Bush. He partnered with David Boies, his adversary in the 2000 Supreme Court decision that put Bush in the White House.
Throughout the case, Olson and Boies argued that the ban discriminated against one segment of the population by denying them the fundamental right to marry and that same sex marriage was no threat to heterosexuals.
PURPOSE OF MARRIAGE
Conservative Charles Cooper led the defense, arguing that it is reasonable to fear that allowing same-sex marriage would undermine heterosexual marriage and self-evident that the purpose of marriage was procreating and raising children.
"You don't have to have evidence" to prove that the purpose of marriage is to bear and raise children, he said in the closing arguments, citing legal precedents.
Months earlier, he had surprised the court by saying he did not know how gay marriage would hurt heterosexuals -- and that he did not need to know in order to win the case.
"At the end of the day, 'I don't know' and 'I don't have to present any evidence,' with all respect to Mr. Cooper, doesn't cut it," responded Olson on Wednesday.
Walker subjected Cooper to a barrage of questions, turning the lawyer's closing arguments into a cross-examination about the purpose of marriage, the state's role, and whether gays deserve special court protection akin to racial minorities.
Cooper contended that the only way to invalidate Prop 8 was to prove there had been absolutely no good reason, or rational basis, for millions of Californians to back it.
Some gay advocates opposed challenging the ban in federal court, fearing that even if they win this round, they are likely to lose in the conservative Supreme Court, setting back their agenda for years.
Walker seemed uncertain whether the nation was ready for such change, alluding to the decades of division sparked by the Supreme Court pro-abortion ruling Roe v. Wade.
Opponents of the same-sex marriage ban compare it to laws which outlawed interracial marriage in some state. Walker noted that the high court ruled on that questions only after many states began reversing their bans.
"Why are we not at that same tipping point here with respect to same-sex marriage?" he asked.
Proponents and opponents of Prop 8 spent a combined $84 million to sway voters, making it one of the most expensive ballot in U.S. history. It passed by 52.5 percent to 47.5 percent. Olson said its passage ultimately was based on fear.
But the judge, who is expected to rule in a few weeks, pressed Olson whether he should second-guess voters. Did not the debate itself prove that there was a good argument to stop gay marriage, he asked.
Citizens could discriminate in their daily lives but could not put that view into law, Olson replied.
(Editing by Alan Elsner)