A California judge has set a date in January 2010 for a lawsuit challenging the state’s ban on gay marriage.

The case, brought by two gay couples who argue the ban violates their constitutional rights, will be heard on January 11th.

US district judge Vaughn Walker told the couples’ lawyers and supporters of the ban to immediately begin exchanging evidence and interviewing each other’s witnesses.

He barred a number of gay rights groups and social conservatives from joining the case, saying both sides were adequately represented.

Walker also appealed to California governor Arnold Schwarzenegger to give his “thoughts and views”. Although Schwarzenegger supports gay marriage, he has said his administration will remain neutral during the case.

The gay couples are being represented by Ted Olson and David Boies. The two have joined forces after going head to head in the Bush v Gore case of 2000. The choice of the pair, with Olson a conservative and Boies a liberal, is seen to make the point that the lawsuit is a human rights issue rather than a case of left against right or Democrat against Republican.

The gay couples are Kris Perry and Sandy Stier, of northern California, and Paul Katami and Jeff Zarrillo, who live in southern California.

Gay marriage was legalised in California in May 2008. However, Prop 8 defined marriage as being between a man and a woman last November. Supporters of gay marriage argued the initiative was unconstitutional and discriminatory.

In May, Supreme Court judges rejected an argument from gay marriage supporters that the ban was unconstitutional but unanimously ruled that the 18,000 gay couples who married while gay marriage was legal will stay wed.