Rupert Cornwell in Washington
A nervous White House is bracing itself for the worst as the inquiry into the leak of the identity of a CIA agent reaches its climax, possibly with the indictment of one or more officials as early as this week.
Every sign is that Patrick Fitzgerald, the special prosecutor, is close to wrapping up his 22-month-old grand jury investigation, in which attention has focused on two top aides - President Bush's adviser Karl Rove and Lewis "Scooter" Libby, the chief of staff to the Vice-President Dick Cheney.
Mr Fitzgerald has lifted a corner of the rug on the bitter struggles before and immediately after the Iraq invasion between Mr Cheney's office and the CIA. The struggles came amid the unravelling of the Bush administration's claims that Saddam Hussein had weapons of mass destruction.
The investigation began after the conservative columnist, Robert Novak, revealed the name of the CIA agent Valerie Plame, whose husband, the retired diplomat Joseph Wilson, was a fierce critic of the war. Mr Novak leaked the name of Ms Plame in July 2003.
As the investigation unfolded, Mr Rove and Mr Libby emerged as key informants of journalists covering the affair, including Judith Miller, the New York Times reporter who spent 85 days in jail after initially refusing to reveal her sources.
Mr Rove has made four appearances before the grand jury in Washington, the most recent of them last Friday, while Ms Miller says she had three conversations with Mr Libby in which Ms Plame was discussed - although she never wrote a story on the subject.
Mr Wilson contends that the revelation of his wife's identity was a deliberate retaliation by the administration, after he had infuriated them with an article in The New York Times in which he publicly debunked the claim that Iraq had been seeking uranium in Africa as part of a revived effort to build nuclear weapons.
Mr Rove and Mr Libby admit to discussing Mr Wilson's wife with journalists, but say they never identified her by name, still less deliberately leaked the fact that she was a covert operative - leaking such information is a crime under United States law.
The prosecutor's office says Mr Fitzgerald, who is based in Chicago, will return to Washington to announce his conclusions. But it is far from certain who will be indicted, and on what charges. Even the date of any announcement is unclear, as the grand jury's term runs until 28 October.
Analysts say it will be very hard to prove the original charge of an organised conspiracy to leak Ms Plame's name and job. More likely, it is believed, are charges of perjury or obstruction of justice, arising from discrepancies in testimony made to the grand jury.
But the consequences for the White House could be devastating. Mr Rove and Mr Libby are the most influential aides of their bosses. If indicted, they would have to take a leave of absence to organise their defence ahead of any trial.
A White House spokeswoman said the inquiry was not overshadowing the administration's work. "It's business as usual," she said.