A federal judge said Thursday he will not delay a 2 1/2-year prison sentence for I. Lewis “Scooter” Libby, a ruling that could send the former White House aide to prison within weeks.U.S. District Judge Reggie B. Walton’s decision will send Libby’s attorneys rushing to an appeals court to block the sentence and could force President Bush to consider calls from Libby’s supporters to pardon the former aide.