But some Homeland Security officials said they did not expect the national threat warning to be raised from yellow - the midpoint on its five-color scale - to orange unless more specific intelligence was received.
Still, U.S. officials are telling holiday travelers to be vigilant about the threat of terrorist attacks, a warning prompted in part by a raised level of ominous intercepted communications that hasn't quieted for months.
The significance of the sustained level of intelligence "chatter" is unclear, the officials said.
Since the Sept. 11, 2001, attacks, analysts have observed a pattern of spikes in the chatter and other threat intelligence suggesting possible new assaults. Those spikes were always followed by periods of relative calm.
But since late summer, that pattern has been broken. The threat intelligence has poured in at a sustained rate, officials said, though it has been frustratingly short of specifics - no credible information to suggest a time, target or method of attack.
"The Department of Homeland Security remains very concerned about the volume of reporting of threats against U.S. interests both here and abroad," said spokesman Brian Roehrkasse. "We continue to encourage our homeland security professionals to be on a heightened state of alert, especially as we enter this busy holiday travel period."
On Friday, the Arabic television network Al-Jazeera aired a new statement from Ayman al-Zawahri, the chief deputy of Osama bin Laden.
In Washington, the CIA said Saturday its analysts believed the tape most likely was a recording of al-Zawahri, a senior intelligence official said, speaking on the condition of anonymity.
And an Egyptian lawyer who knows al-Zawahri, Montasser el-Zayat, said
the broadcast was undoubtedly al-Zawahri's voice.
"We are still chasing the Americans and their allies everywhere, even in their homeland," the voice purported to be al-Zawahri's said.
Some statements from al Qaeda leaders are later regarded as preludes to attacks; others simply propaganda. Al-Zawahri said he was marking the second anniversary of the battle of Tora Bora, the mountainous region of Afghanistan where bin Laden was believed to have escaped U.S. bombs.
Intelligence officials said they don't know what to make of the new pattern in threat chatter - a shorthand term that describes intercepted communications and other intelligence.
The change could mean an attack is in the offing, officials acknowledged.
But it could, instead, be the product of terrorists' efforts to scare people and fool the warning system by making false threats over communications channels, on the assumption that U.S. intelligence will hear them.
Or it could mean nothing at all, the officials said. Some increases in chatter have not been associated with attempted terrorist strikes.
Much of the threat information suggests attacks directed at U.S. interests in Saudi Arabia and Iraq, officials said. The State Department recommended this week that its nonessential diplomatic personnel as well as diplomatic families leave the Saudi kingdom, and a defense official said threat information pointed toward an attack in the next six weeks.
Suicide bombers with links to al Qaeda struck last month in Saudi Arabia and Turkey.
But U.S. officials also believe there is a domestic threat from al Qaeda operatives in the United States.
One senior intelligence official, speaking on condition of anonymity, said analysts are particularly concerned about the threat of Sept. 11-style attacks, in which terrorists would use hijacked airliners as weapons.
A recent warning also was issued about a possible strike using a fuel tanker truck.
Over the past six months, Homeland Security, fearful of spooking Americans unnecessarily, has become more resistant to raising the terror alert level when the general threat information increases.
Still, officials described the intelligence as a reminder to holiday travelers and security personnel to remain vigilant.