Judge Reggie B. Walton, who presided over the trial, has great leeway in fixing a sentence because federal guidelines are no longer as binding as they once were. But they still provide a recommended time range that is reached by a complicated calculation. The probation office calculated the range as 15 to 21 months, Mr. Libby’s lawyers said.

“Distinguished public servant. Generous mentor. Selfless friend,” begins the court filing in which Mr. Libby’s lawyers asked that he be spared prison. “This is the rich portrait of Mr. Libby that emerges from the description of him in more than 160 heartfelt letters submitted to the court on his behalf.”

“There is no denying the seriousness of the crimes of which Mr. Libby was convicted,” the lawyers wrote. “At the same time, there is no denying the kind of person Mr. Libby is and the contributions he has made to his country.”

While the two sides have offered starkly different proposals for Mr. Libby’s sentence, another question to be decided by Judge Walton may be equally important. If he sentences Mr. Libby to prison, he has to decide whether he should begin serving his time immediately or be allowed to remain free pending his appeal. The issue could bear on whether Mr. Libby receives a presidential pardon.

Mr. Libby’s lawyers and other supporters have said President Bush should issue a pardon, and if Mr. Libby is sent to jail on Tuesday, that decision would have to be put immediately in front of the president if a pardon were to have any value. The White House has not commented on the possibility of a pardon.