Tom Ridge, the homeland security secretary, planned to discuss the chance at a midafternoon news conference at the agency's headquarters. A department official confirmed the elevated threat level but declined to provide details before Ridge's appearance.
U.S. officials by the end of last week were telling holiday travelers to be vigilant about the threat of terrorist attacks. The warning was prompted in part by a raised level of ominous intercepted communications that has not quieted for months.
The significance of the sustained level of intelligence "chatter" is unclear, the officials said.
Homeland Security officials said they did not expect a change in the threat level unless more specific intelligence was received.
On Friday, the Arabic television network Al-Jazeera aired a new statement from Ayman al-Zawahri, the chief deputy of Osama bin Laden. The CIA said Saturday it believes the tape is authentic.
"We are still chasing the Americans and their allies everywhere, even in their homeland," according to the voice on the tape.
Some statements from al-Qaida leaders are later regarded as preludes to attacks; others simply propaganda.