After days of expressing confidence about the documents used in a "60 Minutes'' report that raised new questions about President Bush's National Guard service, CBS News officials have grave doubts about the authenticity of the material, network officials said last night. Those officials, who asked not to be identified, said CBS News would most likely make an announcement as early as today that it had been deceived about the documents' origins, and that it was mounting an intensive news investigation of where they came from. But these people cautioned that CBS News could still pull back from an announcement. Officials...