"I'm the guy they used to call Deep Throat," Felt, who is now 91 and living in California, told Vanity Fair in an article published Tuesday.

Family members of the former Federal Bureau of Investigation official told reporters outside Felt's home in the California town of Santa Rosa that he was relieved to finally be able to speak out and see the 30-year veil of secrecy lifted.

Bob Woodward, the Washington Post reporter whose clandestine briefings by the world's most celebrated anonymous source in an underground garage helped unravel the Watergate cover-up, at first declined to confirm the identity.

Woodward and fellow Post reporter Carl Bernstein had always maintained that they would only reveal "Deep Throat's" identity after the source's death.

But the two reporters and their editor of the time, Benjamin Bradlee, said they had decided to confirm the identity following the family's statement.

"W. Mark Felt was 'Deep Throat' and helped us immeasurably in our Watergate coverage. However, as the record shows, many other sources and officials assisted us and other reporters for the hundreds of stories that were written in The Washington Post about Watergate," Woodward and Bernstein said in a statement.

Bradlee, who was the Post's executive editor during Watergate, said: "The thing that stuns me is that the goddamn secret has lasted this long."

Reading a family statement, Felt's grandson, Nick Jones, described his grandfather as "a great American hero who went well and above the call of duty at much risk to himself."

"We all sincerely hope the country will see him this way, as well," Jones said, adding that Felt was pleased at finally being "honored for his role as 'Deep Throat'."

Felt's name was no stranger to the perennial Washington dinner party game of identifying Woodward's source.

The list of likely suspects has included former Nixon White House aide Diane Sawyer, who is now a television presenter, Nixon's chief of staff Alexander Haig and FBI director of the time Patrick Gray.

Some even argued that "Deep Throat" was in fact several people, or merely a literary invention.

Jones said his grandfather had previously expressed deep reservations about revealing his secret, over concerns that his actions would not have been deemed appropriate for an FBI official.

"But as he recently told my mother, I guess people used to think 'Deep Throat' was a criminal. But now they think he's a hero," he said.

Felt's family had no idea of his secret until 2002, when Felt's close friend and frequent social companion, Yvette La Garde, told his daughter Joan that Felt had confided to being Woodward's source.

The Vanity Fair article said Joan confronted her father, who initially denied it, but after she explained La Garde's disclosure responded: "Since that's the case, well, yes I am."

"Deep Throat" met with Woodward several times to help break stories about the involvement of Nixon administration officials in the June 17, 1972, burglary of the Democratic National Committee headquarters at the Watergate complex in Washington.

The burglars, who were seeking to plant listening devices to spy on the Democrats during an election campaign, were tried and found guilty.

With public pressure mounting over his deceit, Nixon became the first US president to resign in August 1974.

Watergate made celebrities of Woodward and Bernstein, whose exploits were immortalised in the 1976 movie "All The President's Men".

Part of the enduring appeal of the "Deep Throat" mystique was the decision to name him after the culturally iconic porn film of the same name.

Following Felt's disclosure, his daughter Joan told Vanity Fair she had pleaded with him to announce his role immediately so that he could have some closure, and accolades, while he was still alive.

Joan recounted how she tried to elicit further information from her father as they were watching a Watergate TV special.

When his name came up as one of the possible "Deep Throat" candidates, she said she deliberately questioned her father in the third person.

"Do you think Deep Throat wanted to get rid of Nixon?" she asked.

"No, I wasn't trying to bring him down," Felt responded, insisting that he was "only doing his duty".

Felt finally conceded to family pressure to go public when his daughter persuaded him that that the story could bring some financial benefit that would help pay for his grandchildrens' education.