The conclusion suggests that the group that launched the most devastating terror attack on the United States has been able to rebuild despite nearly six years of bombings, war and other tactics aimed at crippling it.
Still, numerous government officials say they know of no specific, credible threat of a new attack.
A counterterrorism official familiar with a five-page summary of the new government threat assessment called it a stark appraisal that will be discussed at the White House on Thursday as part of a broader meeting on an upcoming National Intelligence Estimate.
The official and others spoke on condition of anonymity because the secret report remains classified.
Counterterrorism analysts produced the document, titled "Al Qaeda better positioned to strike the West." The document pays special heed to the terror group's safe haven in Pakistan and makes a range of observations about the threat posed to the United States and its allies, officials said.
Al Qaeda is "considerably operationally stronger than a year ago" and has "regrouped to an extent not seen since 2001," the official said, paraphrasing the report's conclusions. "They are showing greater and greater ability to plan attacks in Europe and the United States."
The group also has created "the most robust training program since 2001, with an interest in using European operatives," the official quoted the report as saying.
At the same time, this official said, the report speaks of "significant gaps in intelligence" so U.S. authorities may be ignorant of potential or planned attacks.
John Kringen, who heads the CIA's analysis directorate, echoed the concerns about al Qaeda's resurgence during testimony and conversations with reporters at a House Armed Services Committee hearing on Wednesday.
"They seem to be fairly well settled into the safe haven and the ungoverned spaces of Pakistan," Kringen testified. "We see more training. We see more money. We see more communications. We see that activity rising."
The threat assessment comes as the National Intelligence Council is preparing a National Intelligence Estimate focusing on threats to the United States. A senior intelligence official, who spoke on condition of anonymity while the high-level analysis was being finalized, said the document has been in the works for roughly two years.
Kringen and aides to National Intelligence Director Mike McConnell would not comment on the details of that analysis. "Preparation of the estimate is not a response to any specific threat," McConnell's spokesman Ross Feinstein said, adding that it would be ready for distribution this summer.
Counterterrorism officials have been increasingly concerned about al Qaeda's recent operations. This week, Homeland Security Secretary Michael Chertoff said he had a "gut feeling" that the United States faced a heightened risk of attack this summer.
CBS News chief Washington correspondent Bob Schieffer explained that Chertoff will face a "fierce reaction" from Democrats if his warning is fueled by more than a "gut feeling."
Al Qaeda and its sympathizers have shown an interest in summertime attacks. Some examples from recent years: