A federal judge in Oklahoma City rejected a plea for leniency for Michael Fortier, the man who never warned the authorities about the Oklahoma City bombing three years ago, but who later became a leading government witness against the two men who were convicted. The judge indicated that he might impose a harsher sentence on Fortier than the 11 to 14 years suggested by prosecutors. Fortier has pleaded guilty to failing to warn officials about of the plot, to lying to the FBI, and to two charges involving the transportation of stolen firearms.