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.

The 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. CBS News has already begun intensive reporting on where they came from, and people at the network said it was now possible that officials would open an internal inquiry into how it moved forward with the report. Officials say they are now beginning to believe the report was too flawed to have gone on the air.

But they cautioned that CBS News could still pull back from an announcement. Officials met last night with Dan Rather, the anchor who presented the report, to go over the information it had collected about the documents one last time before making a final decision. Mr. Rather was not available for comment late last night.

--The New York Times