Charges could come as early as Wednesday in the leak of a CIA officer's identity.
Special Counsel Patrick Fitzgerald is wrapping up a two-year criminal investigation.
Lawyers for key White House officials expect him to decide as early as today whether to charge Vice President Dick Cheney's chief of staff, Lewis "Scooter" Libby. Presidential political adviser Karl Rove also could face charges.
Fitzgerald has been in Washington since Monday, and lawyers close to the investigation say he has dispatched FBI agents to conduct additional interviews.
The grand jury Fitzgerald has used in the investigation is set to expire Friday.