WASHINGTON — I. Lewis "Scooter" Libby, once the top aide to Vice President Dick Cheney, saw his hopes of avoiding prison in the CIA leak case begin to dim yesterday as a federal judge ruled he could face a longer sentence because the investigation he obstructed was so serious.Special Prosecutor Patrick Fitzgerald wants to put Libby in prison for up to three years because the investigation he obstructed — the leak of a CIA operative's identity — was so serious.

"We need to make the statement that the truth matters ever so much," Fitzgerald said.

Libby's attorneys are seeking no jail time and argue that it is unfair to increase the sentence simply because the investigation was serious.

US District Judge Reggie B. Walton determined, however, that the seriousness of an alleged crime must be considered in sentencing.

Libby, the highest-ranking US official convicted of a crime since the Iran-Contra affair in the mid-1980s, was convicted of lying to investigators about what he told reporters regarding CIA operative Valerie Plame. Her identity was leaked to reporters in 2003 after her husband began criticising the Bush administration's war policies. Neither Libby nor anyone else was charged for leaking Plame's name.

Walton's preliminary ruling does not predict Libby's sentence but makes it harder for Libby's attorneys to argue for no jail time because it raises the seriousness of his offence.

Theodore Wells, another of Libby's defence attorneys, urged Walton to consider Libby's career of government service. Before joining the White House staff, Libby served in the State and Defence departments and is known as an expert on weapons of mass destruction and biological threats.

"There are a lot of lawyers, people who go to law school, who come from privileged backgrounds, who do squat for their country, who do nothing for others," Wells said.

In support of Libby's bid for probation, dozens of prominent people wrote letters to Walton. Among the letter writers were former Defence Secretary Donald H. Rumsfeld; Marine Gen. Peter Pace, chairman of the Joint Chiefs of Staff; former Secretary of State Henry Kissinger; and John Bolton, former US ambassador to the United Nations.

"My hope and prayer is that his outstanding record, his many contributions to our country and his value as a citizen will be considered carefully," Rumsfeld wrote.

Libby was to have the opportunity to speak publicly about the charges later in the day. He has not discussed the case since his 2005 indictment. Throughout his month-long trial, and following his conviction in March, he always let his lawyers do the talking.

Defense attorneys have not said whether Libby would speak. It's a delicate decision, one made more difficult because Libby has maintained his innocence and is appealing his conviction.

"The only thing any sentencing judge wants to hear is remorse, and if they don't think it comes from the heart or they think they're only sorry for getting caught, for losing their job, or for going to jail, it doesn't count," said Hugh Keefe, a Connecticut defence attorney who teaches trial advocacy at Yale University.

He cannot offer too much of an apology, however, without jeopardising his appeal. A general apology, one in which Libby expresses regret for the drawn-out litigation and the pain he has caused his family, leaves him exposed to another Fitzgerald attack for not showing genuine remorse.

"The alternative is, you risk just sitting there silent. What's the judge's reaction to that going to be?" said Michael E. Horowitz, a Washington defence attorney and former Justice Department official.

Former Illinois Gov. George Ryan apologised — generally speaking — to voters last year at his corruption sentencing.

"When they elected me as the governor of this state, they expected better, and I let 'em down, and for that I apologise," Ryan said before a judge sentenced him to 6[1/2] years in prison.

Former Atlanta mayor Bill Campbell said nothing at his sentencing for tax evasion last year and was ordered to spend 2[1/2] years in prison. Former Enron CEO Jeffrey Skilling declared "I am innocent of these charges," before being sentenced to 24 years in prison for corporate fraud.

Walton has a reputation as a tough judge. If he sends Libby to prison, he must decide whether to put that sentence on hold while the appeal plays out.

If Walton should grant such a delay, it would give Bush more time to consider a pardon for Libby.

The president has said he is going to stay out of it until the legal case is over, a decision that is harder if his former aide is headed to prison.