HE HAS been likened to Eliot Ness, the fearless Prohibition-era prosecutor who brought Al Capone to justice. Like Ness, Patrick Fitzgerald hails from Chicago and has a reputation for being meticulous, impartial and relentless.

But Mr Fitzgerald, 44, an independent attorney-general, is not investigating an underworld godfather. He has spent almost two years probing the highest levels of the US Government in an investigation that threatens to land some of the most senior figures at the White House in court. During his inquiry into the leak of a CIA agent’s name to the media, Mr Fitzgerald has privately interviewed President Bush, the Vice-President, Dick Cheney, and a host of their officials.

Washington is abuzz with speculation that, perhaps as soon as this week, Mr Fitzgerald could indict Karl Rove — Mr Bush’s most senior adviser and the man the President calls his “architect” — and Mr Cheney’s chief of staff, Lewis “Scooter” Libby.

Charges could come under espionage laws that prohibit the identification of a secret agent, or perjury laws covering obstruction of justice.

They would plunge Mr Bush deeper into trouble at a time when some of his traditional conservative supporters are already furious at the soaring budget deficit and his nomination of a close friend, Harriet Miers, for the vacant seat on the Supreme Court. If indicted, Mr Rove would be expected to set aside his White House duties until he is cleared.

There are also further inquiries into allegations of financial wrongdoing by Tom DeLay, the Republican leader in the House of Representatives, and Bill Frist, the Republican majority leader in the Senate.

The case that Mr Fitzgerald is examining has its roots in the intelligence that led America to invade Iraq. It centres on the unmasking of Valerie Plame as a CIA agent by journalists shortly after her husband, Joseph Wilson, a former US Ambassador to Gabon, began publicly criticising the White House case for war.

In 2002 Mr Wilson was sent to Niger, a country with which he was familiar, to investigate claims that Iraq had tried to acquire weapons-grade uranium. He satisfied himself that the intelligence was flawed.

But he became a thorn in the President’s side when Mr Bush referred to the Niger uranium plot in his State of the Union speech in 2003 — a year after Mr Wilson had told the CIA that the claims were bogus.

Mr Wilson believes that his wife’s career was deliberately ruined in revenge for his criticism when she was identified as the CIA agent who dispatched him to Niger. Knowingly revealing the identity of a secret agent is an indictable offence and journalists have subsequently told Mr Fitzgerald that Mr Rove and Mr Libby talked to them about the case.

Judith Miller, a New York Times reporter who went to jail for 85 days rather than identify her source for naming Ms Plame, has now told Mr Fitzgerald that Mr Libby spoke with her three times about the case in 2003. Ominously for the White House, Mr Fitzgerald questioned her closely on Mr Cheney’s role in the affair.

There are parallels between Mr Fitzgerald’s investigation and the Hutton inquiry in 2003 into the death of David Kelly, the British weapons inspector. Both cases centre on allegations of an official backlash against troublesome figures who dared to question their governments’ case for war.

There may be lessons from the Hutton inquiry for those on Capitol Hill. Lord Hutton’s investigation aroused fevered speculation that it could spell the end for various ministers, spy chiefs and civil servants. In the event, his report exonerated Mr Blair’s administration.

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