The veteran US anchorman Dan Rather will give his final news broadcast this evening before taking a rather earlier than expected retirement.

Rather departs under a cloud of criticism, after lending his support to a report during the American election campaign that the military service record of President Bush was far from exemplary. It quickly emerged that the report was a hoax based on obviously forged documents.

Rather has been the main presenter of CBS Evening News for 24 years, the longest record of any network newscaster. Now 73, he is not retiring from television altogether but is becoming a full-time reporter for the network’s respected 60 Minutes documentary series.

CBS has the lowest nightly viewing figures of the three main US television networks. Even in his last full week on the air, Rather finished a distant third in the ratings. He is signing off on the 24th anniversary of the day he replaced the legendary Walter Cronkite as CBS's news anchor.

Jim Murphy, the broadcast's executive producer, said that the last show will be a look back at some of the biggest stories that Rather has covered - this time talking about the September 11 attacks, Mr Murphy added ruefully - and will include a brief chat with viewers.

Rather was the narrator of the programme in September which suggested that Mr Bush had received preferential treatment during his National Guard service three decades ago, during the Vietnam War.

Within hours, experts questioned the legitimacy of documents used, and when CBS could not authenticate them, the story’s producer was fired and three CBS News executives were asked to resign.

Conservatives say that the report supported their claims that Rather has a liberal bias. He first fell foul of Republicans in 1974, while still a reporter, after a combative exchange with Richard Nixon during the height of the Watergate scandal. After Rather was applauded when he stood to ask a question, President Nixon said, "Are you running for something?"

The journalist snapped back: "No, sir, Mr President. Are you?"

He was criticised for a bad-tempered interview in 1988 with George Bush Snr, and an ill-considered decision to attend a 2001 Democratic fund-raiser in Texas. But he also scored several scoops, including anchoring the CBS report that aired the first pictures from the Abu Ghraib prison scandal.

A tribute on the CBS News website boasts that in his 50 year career Rather has recorded the assassination of President Kennedy, the civil rights movement, Watergate, and wars in Vietnam and Iraq. He has interviewed hundreds of world leaders ranging from Mother Teresa to Saddam Hussein.

"He has braved hurricanes, waded through flood waters, dodged bullets, comforted wounded GIs, mouthed off to presidents, wept on camera, become a lightning rod for conservatives and been badly beaten by a dangerous maniac on Park Avenue," the tribute continues.

"This road well traveled has been strewn with Ratherisms, folksy sayings that can make one smile or wince or both. It was Rather who told us that the Florida presidential race was 'hotter than a Times Square Rolex' and who reminded us of the importance of swing states: 'It don't mean a thing if they don't get those swings'."

Partly because he attracts extreme opinions, Rather is departing without the wave of goodwill that accompanied Tom Brokaw’s exit as anchor of the rival NBC network last year.

After some debate, CBS is also planning to broadcast a prime-time tribute tonight: Dan Rather: A Reporter Remembers. At least one CBS-affiliated station, WWTV in Cadillac, Michigan, has said it might not broadcast the tribute due to viewer complaints.

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