By Byron Kaye

SYDNEY, March 20 (Reuters) - An Australian court on Tuesday threw out part of News Corp's defence against a defamation lawsuit by Geoffrey Rush, a win for the Oscar-winning actor who objected to a series of newspaper articles accusing him of inappropriate conduct.

Rush is suing News's Australian arm over a series of articles in 2017 saying he was the subject of an unspecified complaint to Sydney Theatre Company in relation to a 2015 production of King Lear where he played the starring role.

News is defending itself, arguing it should be allowed to publish the articles because they were based on the truth. News sought a court order that the theatre company produce a copy of the complaint, but Rush sought to stop that order.

In an intermediary ruling, Federal Court Judge Michael Wigney dismissed the News request, saying that for the theatre company to hand over the complaint after the articles were published would have "no apparent forensic purpose".

"A defendant who pleads (the truth) must do so on the basis of the information which it has in its possession when the defence is delivered, and is not permitted to undertake a fishing expedition in the hope of finding something in support of its plea," Wigney wrote in his ruling.

Wigney ordered News to amend its defence and to pay Rush's legal costs from requesting the change.

Rush, who won the Best Actor Oscar in 1997 for "Shine" and has since appeared in the "Pirates of the Caribbean" movies and Best Picture Oscar winners "Shakespeare In Love" and "The King's Speech", has denied wrongdoing and said he was never told of the complaint at the time.

He has said the timing of the articles, late 2017, suggested he had committed sexual assault or inappropriate conduct in the theatre because other articles in the weeks before had named producer Harvey Weinstein and actor Kevin Spacey as "sexual predators who had committed acts of sexual assault and/or sexual harassment", Wigney wrote.

Rush is seeking damages and a restraint on further publication on the matter. He has stepped down as president of the Australian Academy of Cinema and Television until the matter is resolved.

The case continues at a date to be determined. (Reporting by Byron Kaye; Editing by Michael Perry)