Political opponents of U.S. President George Bush are blasting him for commuting the sentence of a former top aide to Vice President Dick Cheney convicted in the "Plamegate" affair.

House of Representatives Speaker Nancy Pelosi said Monday that Bush's actions showed he "condones criminal conduct."

"Libby's conviction was the one faint glimmer of accountability for White House efforts to manipulate intelligence and silence critics of the Iraq war," said Senate Majority Leader Harry Reid.

"Now, even that small bit of justice has been undone."

A judge sentenced 56-year-old I. Lewis "Scooter" Libby, who had been Cheney's chief of staff, to 2� years in June. Hours earlier on Monday, a federal appeals court panel ruled Libby couldn't delay his prison term in the case that originally stemmed from the leaking of a CIA operative's name.

"I respect the jury's verdict," Bush said in a statement. "But I have concluded that the prison sentence given to Mr. Libby is excessive. Therefore, I am commuting the portion of Mr. Libby's sentence that required him to spend thirty months in prison."

Libby will still have to pay a US$250,000 fine, serve two years of probation and have a criminal record. Bush said his decision still "leaves in place a harsh punishment for Mr. Libby.

"The reputation he gained through his years of public service and professional work in the legal community is forever damaged. His wife and young children have also suffered immensely. He will remain on probation. The significant fines imposed by the judge will remain in effect. The consequences of his felony conviction on his former life as a lawyer, public servant, and private citizen will be long-lasting."

Many Libby supporters happy

Libby supporters celebrated the president's decision.

"President Bush did the right thing today in commuting the prison term for Scooter Libby," said House Republican Whip Roy Blunt of Missouri.

"That's fantastic. It's a great relief," said former ambassador Richard Carlson, a fundraiser for Libby's defence fund.

"Scooter Libby did not deserve to go to prison and I'm glad the president had the courage to do this."

A spokeswoman for Cheney said: "The vice-president supports the president's decision."

Other conservatives, however, insisted Libby deserved a full pardon.

In his statement, Bush noted that while Libby was a first-time offender who had years of public service, an argument used by Libby supporters, he must be held accountable for his crimes.

A jury found Libby guilty in March of lying to authorities and obstructing the investigation into the leak of Valerie Plame's identity.

Plame was an active CIA operative, and revealing the identity of such operatives is illegal; however, no one has ever been charged in connection with that act.

She is the wife of Joseph Wilson, a former U.S. diplomat. In 2002, the CIA asked Wilson to look into an alleged purchase by Iraq of uranium yellowcake from the African country of Niger. Wilson found the claim to be dubious In the run-up to the March 2003 invasion of Iraq, Bush claimed in his Jan. 28, 2003  State of the Union speech that the Iraqi government of dictator Saddam Hussein had sought uranium.

Wilson attacked what he saw as the Bush administration's twisting of intelligence in a July 6, 2003 newspaper commentary. Syndicated newspaper columnist Robert Novak then revealed the information about Plame.

Libby is the highest-ranking White House official ordered to prison since the Iran-Contra affair of the 1980s.

The federal prosecutor in Libby's case is Patrick Fitzgerald. His office is handling the current prosecution of Canadian-born media tycoon Conrad Black. A jury is deliberating that case in Chicago.

Fitzgerald issued a statement saying: "An experienced federal judge considered extensive argument from the parties and then imposed a sentence consistent with the applicable laws. It is fundamental to the rule of law that all citizens stand before the bar of justice as equals."

With files from The Associated Press