Lawyers for former US vice-presidential aide I. Lewis "Scooter" Libby asked a federal judge Thursday to delay Libby's prison sentence because they felt they have a good chance of winning an appeal of his conviction. Libby was found guilty of perjury and obstruction of justice in March, and sentenced to 2 1/2- years in prison on Tuesday.

Defense lawyers filed papers with the court Thursday arguing that Special Prosecutor Patrick Fitzgerald did not have the authority to bring charges against Libby, and that they were wrongly barred from questioning NBC reporter Andrea Mitchell about certain aspects of the Valerie Plame scandal. Earlier this week, US District Judge Reggie B. Walton said there was no reason that Libby should not begin serving his sentence while his case is on appeal.