Woodward, the Washington Post reporter who broke the Watergate scandal that forced President Richard Nixon out of office, has refused publicly to divulge the name of his informant without permission, which has thus far been withheld.

The naming of CIA agent Valerie Plame as the wife of Joseph Wilson, the former US ambassador sent to Niger to investigate disputed claims that Saddam Hussein was trying to purchase uranium yellowcake for the manufacture of nuclear weapons, led to the indictment last month of Vice-President Dick Cheney’s top aide, Lewis “Scooter” Libby, for lying to a grand jury.

It is an offence in America to reveal the identity of a covert agent, although doubts remain about Plame’s precise status.

A spokeswoman for the National Security Council (NSC) denied that Hadley was the journalist’s source. However, in South Korea on Friday during an official visit with President George W Bush, Hadley dodged the question.

“I’ve also seen press reports from White House officials saying that I am not one of his sources,” Hadley said with a smile. Asked if this was a yes or no he replied: “It is what it is.”

A White House official said the national security adviser’s ambiguity was unintentional and repeated that Hadley was not Woodward’s source. But others close to the investigation insisted that he was.

If so, according to Woodward’s timeline, he will have disclosed the information in mid-June 2003, roughly a week before Libby talked to other reporters on June 23. Supporters of Cheney’s disgraced aide are jubilant that this casts doubt on special prosecutor Patrick Fitzgerald’s contention that Libby was the first to spread the word about Plame.

When Woodward realised this, he went back to his informant. “My source said he or she had no alternative but to go to the prosecutor. I said, ‘If you do, am I released?’ The source said yes, but only for the purpose of discussing it with Fitzgerald.” Woodward testified under oath to the special prosecutor last Monday.

Woodward said the unnamed official told him about Plame in “an offhand, casual manner . . . almost gossip” and “I didn’t attach any importance to it”. He never wrote up the story.

With more journalists in the loop than previously identified, it will be harder for Fitzgerald to prove Libby was deliberately lying when he said he first learnt of Plame from a journalist rather than the CIA.

Two years ago, when Plame’s identity was first revealed, Hadley was Condoleezza Rice’s deputy at the NSC. He is also thought to have been a key source for two books by Woodward on the aftermath of the 9/11 attacks.

Other potential suspects have been denying they are Woodward’s source. Cheney has come under suspicion, although sources close to the investigation claim he is not in the frame.

Fitzgerald may want to interview Woodward’s informant and declared in court filings on Friday that proceedings would continue under a new grand jury. Supporters of Karl Rove, the top White House adviser known as “Bush’s brain”, also fear Fitzgerald may still be investigating him.

Woodward declined to confirm or deny that Hadley had leaked him the information.

It is familiar territory for the Washington Post journalist, who kept the name of Deep Throat, his Watergate informant, secret for more than three decades until Mark Felt, the former deputy director of the FBI, outed himself this year.

Yet colleagues at the Washington Post have been criticising him on their internal message board. One accused Woodward of being the “800-pound elephant in the room”, adding: “I admire the hell out of Bob, but this looks awful.”

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