Scooter Libby should not be pardoned. But his punishment — 30 months in prison, two years' probation and a $250,000 fine — is excessive. President Bush should commute the sentence by eliminating the jail term while preserving the fine.

There is a legal principle at stake in this case greater than either Libby or the politics of the moment. It is a fundamental rule of law that the grand jury is entitled to every man's evidence. The grand jury cannot survive as the essential truth-finding tool it is if witnesses can lie with impunity. True, Libby committed a "process crime" — that is, so far as has been established in court or even alleged by the prosecutor, he committed no crime until after the government initiated its investigation of the underlying act (namely, the revelation of Valerie Plame's CIA employment). But for obvious reasons it is not for grand jury witnesses to determine when an investigation is legitimate. As the Supreme Court has noted, there are many ways to challenge questions one believes the government should not be asking, but "lying is not one of them."

U.S. District Judge Reggie Walton noted that there was ample evidence that Libby intentionally lied. Jurors took care (they did not convict on all counts), and the evidence before them makes it hard to believe that Libby's misstatements were merely a product of poor memory or confusion. The case was proved, and the conviction should not simply be wiped away.

Yet the sentence is another matter. Neither vindication of the rule of law nor any other aspect of the public interest requires that Libby go to prison. He is by no stretch a danger to the community, as "danger" is commonly understood. He did not commit his crime out of greed or personal malice. Nor is his life one that bespeaks a criminal turn of mind. To the contrary, as letters to the court on his behalf overwhelmingly established, he has been a contributor to his community and his country. And whether or not we agree, we cannot dismiss out of hand the notion that Libby thought he was serving his country by his overall conduct in this episode, specifically by letting it be known, truthfully, that it was not the White House that tapped Joseph Wilson to look into whether Saddam Hussein had sought uranium in Niger.

A sense of proportionality argues in favor of eliminating Libby's prison term. This was an unusually harsh sentence for a first offender convicted of a nonviolent and non-drug-related crime. Sandy Berger, national security adviser to President Bill Clinton, was not sentenced to prison for sneaking documents out of the National Archives, destroying them and then lying to investigators. For his actions, Berger received no jail time, a fine one-fifth of that imposed on Libby and 100 hours of community service.

To pardon Libby would not be consistent with the imperative that the mechanisms of law be able to demand, and receive, the truth. But to leave the sentence undisturbed would be an injustice to a person who, though guilty in this instance, is not what most people would, or should, think of as a criminal. Commutation offers a middle ground. Unlike a pardon, commuting the prison sentence would not erase the conviction. It would leave Libby with the disabilities of a convicted felon. But commutation would alleviate the harshest, and unnecessary, aspects of the sentence.

A partial commutation would send the message that we insist on being truthful, but in the name of a justice that still cares about individual circumstances, we will not insist on being vindictive.

William Otis, a former federal prosecutor, was a member of the Attorney General's Advisory Committee on the Sentencing Guidelines under administrations of both parties. He was special counsel for President George H.W. Bush. He wrote this commentary for The Washington Post.