SAN FRANCISCO — A judge on Wednesday said he wants a federal lawsuit challenging California's same-sex marriage ban to go to trial on Jan. 11, proceedings that will showcase expert witnesses on topics ranging from parenting to the relative political influence of gays.

In setting the hastened timetable, U.S. District Judge Vaughn Walker called the case "a matter of huge importance for the people of this state" and indicated he would not tolerate legal maneuvers that could delay its resolution.

Walker ordered lawyers for the two unmarried same-sex couples who are serving as plaintiffs in the lawsuit and for the gay-marriage ban's sponsors to immediately start interviewing each other's potential witnesses and exchanging evidence.

With swiftness partly in mind, the judge also barred several advocacy groups from joining the lawsuit.

Before Wednesday's status conference, three gay-rights groups had petitioned to join the plaintiffs' side. A conservative group that opposes giving gays and lesbians the rights of marriage through domestic partnerships asked to intervene on the side of Proposition 8's official proponents.

Walker denied their requests, saying the groups had failed to show that the lawyers already involved in the case would not adequately represent their aims and interests.

Plaintiff attorneys David Boies and Theodore Olson had requested that all those parties be excluded, saying their participation would needlessly complicate and slow the case.

"Nothing in the record before the court shows the current parties are incapable of delivering a full record that represents all of the parties' interests," the judge said.

Walker did, however, allow the city of San Francisco to join the case, but only to assess the financial impact that withholding the right to wed from same-sex couples has on local governments.

Chief Deputy City Attorney Terry Stewart said that during the trial, the city planned to call witnesses who could testify about the public-health costs of treating gays and lesbian families who feel discriminated against.

He also ordered California Attorney General Jerry Brown's office to work with the city's lawyers in providing testimony on how the voter-approved measure affects state government.

Brown was named as a defendant in the case, but has taken the rare step of refusing to argue for upholding the voter-approved ban.

Proposition 8, which passed in November with 52 percent of the vote, overruled a decision five months earlier by the California Supreme Court that briefly legalized same-sex unions in the state.

The federal lawsuit, which was brought on behalf of the gay couples by Olson and Boies, argues that Proposition 8 must be struck down as discriminatory under the U.S. Constitution. Olson and Boies reiterated Wednesday that they expect the case to eventually reach the U.S. Supreme Court.