Dan Rather has worked at CBS News for more than 40 years (AP)

One of America's most influential news presenters, Dan Rather, has announced that he is to give up his role as the face of CBS News early next year.

The 73-year-old has presented the US network's main evening news broadcast for almost a quarter of a century.

He has faced criticism over a recent report questioning President George W Bush's military service, based on evidence which turned out to be forged.

Mr Rather has said he will continue to work as a correspondent for CBS.

"I have been lucky and blessed over these years to have what is, to me, the best job in the world and to have it at CBS News," he said on Tuesday.

The award-winning journalist has worked at CBS News for more than 40 years and made his name as a reporter covering President Richard Nixon's White House.

"He has been an eyewitness to the most important events and played a crucial role in keeping the American public informed about those events and their larger significance," CBS Chairman Leslie Moonves said.

Mr Rather came into conflict with the Bush administration in the run-up to the US election over a documentary suggesting that the president had not fulfilled his National Guard service during the Vietnam war.

Correspondents say the incident gave ammunition to his conservative critics, who have long accused him of a liberal bias.

He made no mention of the National Guard story in announcing the change, although he acknowledged the controversial report had become a "hippopotamus in the bathtub".

Mr Rather's move comes just before longtime rival Tom Brokaw retires from NBC Nightly News in December.

It leaves Peter Jennings of ABC's World News Tonight as the last of the triumvirate who ruled network news for more than 20 years.

(Agencies)

eyewitness : a spectator who can describe what happened（目擊者，見證人）

ammunition: information that can be used to attack or defend a claim or argument or viewpoint（炮彈）