* Murdoch due in London to address staff anger

By Kate Holton and Mark Hosenball

LONDON, Feb 15 (Reuters) - An investigation into Rupert Murdoch's top-selling British newspaper, the Sun, has uncovered evidence that it paid tens of thousands of pounds in retainers to public officials for tipoffs, a source with knowledge of the probe said on Wednesday.

Much of the evidence passed to police has been provided by Murdoch's own News Corp group, and deepens a crisis at the Sun, where officers have arrested nine former and current senior staff in recent weeks over illegal payments.

Murdoch has been trying to regain the high ground ever since an outcry last summer - over revelations that his journalists had hacked the voicemails of crime victims and their families - forced him to close the profitable News of the World title and abort a planned multibillion-dollar buyout of Britain's biggest satellite broadcaster.

"This is not about sources or expenses, this is an investigation into serious suspected criminality over a sustained period," the source said, speaking on condition of anonymity.

"It involves regular cash payments totalling tens of thousands of pounds a year for several years to public officials, some of whom were effectively on retainers to provide information. In totality it involves a six-figure sum."

News Corp and the police both declined to comment.

Murdoch himself is due in London on Thursday and expected at the Sun on Friday to try to quell a backlash from staff who have accused News Corp and police, as well as the octogenarian himself, of conducting an unparalleled witch hunt into journalists and their sources.

JOURNALISTS FEEL BETRAYED

Much of the anger within News International, Murdoch's British newspaper arm grouping the Times and Sunday Times along with the Sun, is directed at the unit set up by News Corp to root out evidence of illegal behaviour.

The Management and Standards Committee (MSC) was set up at the height of the earlier furore over phone hacking and was designed to rescue the company's reputation and show that it was cooperating with the police.

It includes the award-winning journalist Will Lewis, previously editor of the Daily Telegraph, and reports to Joel Klein, who in turn reports to News Corp board member Viet Dinh.

"Viet Dinh, speaking for the board, was clear from the outset: the investigation would be thorough, independent and go where the facts and evidence led them and let the chips fall where they may," said another source close to the internal investigation.

"So it should come as no surprise that Dinh, Joel Klein and the MSC have been doing exactly what they said they would do."

The close relationship between the MSC and police, where officers work out of the same building with the lawyers and forensic experts of the MSC, has infuriated the newspaper journalists who feel they have been hung out to dry.

Britain's two most senior police officers quit last year over their handling of the phone hacking scandal and a number of serving officers have also been detained in the investigation into payments to officials.

"The management has done nothing to protect us from this appalling invasion of our work," one company insider told Reuters. "Nobody has said, 'You can't do this to journalists'. A lot of people are angry."

The National Union of Journalists said it had been approached by News International staff who were looking into whether they could legally challenge the authority of the MSC.

Reuters is a competitor of Dow Jones Newswires, a unit of News Corp.

• A Permanent Economic Emergency