Both the U.S. Supreme Court and Gov. John Ashcroft refused Wednesday to block the execution of murderer Gerald Smith, which was scheduled for early today. The Supreme Court, in a 7-2 decision Wednesday evening, refused to grant a stay of the execution that had been requested by the Missouri Capital Punishment Resource Center, a group that aids lawyers of condemned prisoners in Missouri. The court also refused to allow the group to enter the case on Smith's behalf. Justices William J. Brennan Jr. and Thurgood Marshall dissented.  Also Wednesday, Ashcroft rejected a request to delay the execution to allow court hearings on the allegations involving Smith's brother. 