The officials, speaking on the condition of anonymity, said the conclusion of the Muslim hajj holiday period had played a role in the decision to lower the threat level from orange, the second-highest level on the five-part scale.
Counterterrorism officials had said a significant amount of intelligence pointed toward an attack during that time period.
In addition, other, unspecified intelligence suggested that an attack was somewhat less imminent, the officials said, speaking on the condition of anonymity.
A "yellow" alert is the third-highest alert on a five-step scale. It means the intelligence suggests a "significant" risk of terrorist attacks. The "orange" alert is a step higher and means there's a "high" risk of an attack. The highest alert level is red.
The level was raised to orange on Feb. 7, prompting the government and the private sector to impose extra security measures.
But no attack happened, and it is possible the intelligence was incorrect or misinterpreted.
It is also possible that enhanced security measures or other factors caused the terrorists to change their plans.
An official announcement was expected later Thursday.
Law enforcement, intelligence and homeland security officials debated for days about the proper time to lower the alert status as chatter among suspected terrorist waned and some leads on possible threats were discredited.
The discussions were held in the shadows of a potential war with Iraq, which is expected to increase the risk of terror attacks against Americans.
As recently as Monday, Attorney General John Ashcroft said there were no plans to lower the national alert level.
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