SAN FRANCISCO – The lawyers in the landmark federal trial over the constitutionality of California’s gay marriage ban may have to check their dazzling oratory at the door during next week’s closing arguments.

The presiding judge wants them to answer 39 questions before he delivers his verdict.

Chief U.S. Judge Vaughn Walker has already heard 12 days of testimony in the civil rights case, which is expected to reach the U.S. Supreme Court.

Walker has absorbed the opposing attorneys’ written summaries and amassed a pile of competing briefs from outside groups on the limits of federalism and individual freedom.

Now, after a 4½-month hiatus, he is scheduled on Wednesday to wrap up the trial. Last week, he distilled his thinking about the case to a list of questions — 12 each to lawyers representing gay rights advocates and the ban’s sponsors, and another 15 he wants both sides to address before he later rules.

From former U.S. Solicitor General Theodore Olson, who will be arguing on behalf of two same-sex couples, Walker wants to know what empirical proof there is that allowing gays to marry would reduce discrimination against them.

The judge expects to hear, too, whether he can find that withholding marriage from gays constitutes unlawful discrimination if voters “genuinely but without evidence” believed there were legitimate reasons to limit marriage to a man and a woman.

His questions for Charles Cooper, representing the ban’s sponsors, are equally precise.

What evidence have they produced to support their claim that same-sex marriage would have negative consequences to the institution of marriage? Conversely, how does denying marriage to gays and lesbians improve the odds that children born in California will be raised by a married mom and dad?

Sharp inquiry “is very much typical of this judge,” observed Olson, who frequently was interrupted by Walker during his opening statement in January. “He has done his homework, he is very much involved in this case.”

“It just shows the judge is really grappling with the issues,” agreed James Campbell, another lawyer for the coalition of religious and conservative groups that put Proposition 8 on the November 2008 ballot.

Both lawyers said they found the judge’s punch list to be evenhanded and do not get a sense from it how he is leaning.

The veteran jurist, a Republican appointee, has indicated he does not plan to rule from the bench. Lawyers say they are preparing for him to hand down his ruling within weeks after the closing arguments.

Walker is being asked to overturn the 2008 ballot measure that outlawed same-sex marriages in California five months after the state Supreme Court legalized it and after some 18,000 couples nation had married.