President Bush is facing a firestorm of criticism from Democrats after commuting the sentence of a former aide in his White House, I. Lewis Libby Jr., who was facing 2 1/2 years in prison for obstructing an investigation into the leak of a CIA officer’s identity.

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

Mr. Bush’s action was sought by Libby’s allies, many of them political conservatives with Washington experience, who considered the prosecution of the former chief of staff to Vice President Cheney a miscarriage of justice. The anger among Democrats seemed likely to do little political harm, as the president’s approval ratings are at record lows. What will become clear in the coming days is whether the president’s conservative political base outside Washington welcomes the move as a muscular rebuff to the White House’s critics or regards it as a dubious act of loyalty to a close aide.

The president issued the commutation just hours after a federal appeals court panel unanimously rejected Libby’s bid to remain free while he appealed his convictions for obstruction of justice, false statements, and perjury.

If Mr. Bush had not intervened, Libby would likely have been required to report to prison within the next few weeks. The president did not disturb a $250,000 fine and two years of probation that the trial judge, Reggie Walton, also imposed on Libby, who uses a nickname, “Scooter.”

“My decision to commute his prison sentence leaves in place a harsh punishment for Mr. Libby,” Mr. Bush said. “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.”

The special prosecutor who brought the case, Patrick Fitzgerald, issued a statement last night disputing Mr. Bush’s description of Libby’s sentence as “excessive.”

“The sentence in this case was imposed pursuant to the laws governing sentencings which occur every day throughout this country,” Mr. Fitzgerald said. “In this case, 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. That principle guided the judge during both the trial and the sentencing.”

The prosecutor said he was not commenting on Mr. Bush’s decision to grant the commutation. Spokesmen for Mr. Fitzgerald and the Justice Department did not respond to questions about whether the White House consulted with the prosecutor before Mr. Bush acted.

Furious Democrats accused Mr. Bush of undermining the judicial system. “One of the principles our forefathers fought for was equal justice under the law. This commutation completely tramples on that principle,” Senator Schumer said in a written statement.

The party’s major presidential candidates also denounced the commutation. “Today’s decision is yet another example that this Administration simply considers itself above the law,” Senator Clinton said in a written statement last night. “This commutation sends the clear signal that in this Administration, cronyism and ideology trump competence and justice.”

Senator Obama of Illinois struck a similar tone. “This decision to commute the sentence of a man who compromised our national security cements the legacy of an Administration characterized by a politics of cynicism and division, one that has consistently placed itself and its ideology above the law,” he said

Most of the Republican presidential candidates weighed in with statements of approval. “After evaluating the facts, the President came to a reasonable decision and I believe the decision was correct,” Mayor Giuliani said.

“While for a long time I have urged a pardon for Scooter, I respect the President’s decision. This will allow a good American, who has done a lot for his country, to resume his life,” a former senator who is considering a White House bid and served on Libby’s fund-raising committee, Fred Thompson, said.

Mr. Fitzgerald, who was appointed to investigate the leak to the press of the identity of a CIA operative, Valerie Plame, never brought charges against anyone for leaking. However, Libby was charged with obstructing the probe by lying about when and from whom he learned of Ms. Plame’s CIA tie. A jury convicted Libby in March on one count of obstruction of justice, two counts of lying to a grand jury, and one count of lying to the FBI.

There are no published polls directly addressing how the public will react to a commutation of Libby’s sentence. However, a CNN/Opinion Research Corporation survey taken last month found 72% of Americans opposed a pardon for Libby and only 19% favored one.

Mr. Bush made the announcement as much of Washington was on vacation or preparing for the Independence Day holiday. One challenge for Democrats who may wish to capitalize on the story is that the president’s clemency powers are virtually unfettered, and no legislation can undo what Mr. Bush has done.

Part of Mr. Bush’s statement took on the detached tone of a wire service story, cataloging the claims of unfairness by Libby’s allies and the comments by Libby’s critics underscoring the seriousness of making false statements under oath. Among the arguments noted by the president was the assertion that the investigation should have stopped once a deputy secretary of state, Richard Armitage, admitted he leaked Ms. Plame’s name. Mr. Bush did not indicate whether he agreed or disagreed with most of the arguments. However, he explicitly rejected claims that the special prosecutor acted rashly or was on a vendetta. “Mr. Fitzgerald is a highly qualified, professional prosecutor who carried out his responsibilities as charged,” he said.

An attorney for Libby, William Jeffress Jr., praised Mr. Bush. “We continue to believe the conviction itself was unjust but are grateful for the president’s action commuting the prison sentence,” the defense lawyer said.

Mr. Bush’s aides painted the commutation as a compromise of sorts because it stopped short of a full pardon that would effectively erase Libby’s conviction. Some of Libby’s allies were irked that no pardon was granted.

“I’m relieved for Scooter,” a member of Libby’s defense trust, Richard Carlson, told The New York Sun. “I’m sorry the president didn’t go forward and pardon him. I’m sorry he’s stuck with enormous legal bills. I’m sorry his reputation is besmirched. I don’t think he deserves that.”

The three appeals court judges who considered Libby’s request for release pending his appeal, David Sentelle, Karen Henderson, and David Tatel, said Libby’s appeal did not seem to raise a “substantial question” of law that would entitle him to bail. Judge Sentelle was appointed to the court by President Reagan, Judge Henderson by President George H.W. Bush, and Judge Tatel by President Clinton.
Libby’s full appeal of his convictions could continue and may take another year or more. The court’s decision put Mr. Bush on the spot because Libby would likely have been required to report to jail within weeks.

Libby’s commutation is the fourth Mr. Bush has granted and the first of a convict who had not yet served prison time.

The pardon power was placed in the Constitution as a check the president could wield against abuses by the judiciary and, to some extent, by his own executive branch. A former pardon attorney at the Justice Department, Margaret Love, said public opinion is the only check on a second-term president’s use of clemency. She noted that a Supreme Court Justice in the 18th century, James Iredell, said a president who misused the power risked “the damnation of his fame to all future ages.”