(Note language in third paragraph. Rewrites with further quotes from court, background on Viacom)

By Lisa Richwine

LOS ANGELES, May 6 (Reuters) - A judge called Sumner Redstone's deposition "strong evidence" that the media mogul knew what he was doing when he ejected an ex-girlfriend from his life, suggesting Redstone has the upper hand in a trial over his mental competence that began on Friday.

Although the 92-year-old billionaire, who has majority control of media companies Viacom and CBS, had some trouble speaking in the deposition and did not respond coherently to certain questions, he was clear on the central issue.

Redstone repeatedly called the ex-girlfriend, Manuela Herzer, a "fucking bitch" in the deposition circulated in the packed courtroom, and accused her of stealing money from him. When asked what he wanted at the end of the trial, Redstone replied: "I want Manuela out of my life. Yeah."

Herzer is suing Redstone over her removal in October as the billionaire's designated health care, arguing that Redstone was not mentally competent at the time he made the decision. Redstone's lawyers say he has difficulty speaking but is mentally fit.

Los Angeles Superior Court Judge David Cowan reviewed Redstone's video deposition privately, and appeared to sympathize with the ailing Redstone.

"He has told me now, best he can, what he wants," said Cowan, who will decide the case without a jury. "That's strong evidence."

"Your burden now is a hard one," Cowan said to Herzer's attorneys, who must prove that Redstone was mentally incompetent when he removed Herzer from his plans.

Pierce O'Donnell, who represents Herzer, responded that Redstone's answers to his own lawyer's questions in the deposition were programmed and rehearsed.

Redstone's attorneys asked Cowan to dismiss the lawsuit and the judge requested both sides submit legal briefs over the weekend, saying he could rule on Monday.

Referring to Redstone, Cowan said: "How can I sit here and say, after listening to that video, no you can't have what you want?"

Speaking to reporters outside court, O'Donnell said he was confident Herzer could defeat the motion to dismiss.

"The question isn't whether made that decision, but why did he make that decision?"

Herzer, wearing a black suit at the first day of the trial held in a windowless courtroom on the sixth floor of a downtown Los Angeles courthouse, showed little emotion throughout the day but shook her head and nodded at various points in the testimony. Redstone's daughter Shari and her son Brandon Korff also attended.

The trial, set to run through May 16, is being closely watched by shareholders of Viacom Inc and CBS Corp . Redstone stepped down as executive chairman of both companies earlier this year, assuaging some investor questions about his influence at the company.