The claims were based on e-mail interviews conducted this week by the London-based magazine Al Majalla with al Qaeda spokesman Thabet bin Qais, the magazine reports in an issue to appear Friday.
The magazine provided The Associated Press with an advance copy of the story.
"The Americans only have predictions and old intelligence left," the magazine quoted bin Qais as saying. "It will take them a long time to understand the new form of al Qaeda."
The magazine quoted bin Qais as saying al Qaeda remains "way ahead of the Americans and its allies in the intelligence war, and American security agencies still are ignorant of the changes the leadership has made."
U.S. officials, speaking on condition of anonymity, said they were aware of the report and that bin Qais has been authorized in the past to communicate messages on behalf of Osama bin Laden's terrorist network. The officials cautioned, however, that e-mail interviews can be difficult to authenticate.
Western officials remain convinced that al Qaeda poses a threat despite the arrests of key figures and the loss of its base in Afghanistan.
The FBI's counterterrorism chief, Pasquale D'Amuro, told a congressional committee in Washington on Tuesday that while al Qaeda may very well be in disarray, "it is a severe threat to this nation."
Top legal and security officials from the United States and seven other major nations, meeting this week in Paris, said al Qaeda has apparently moved its operational centers to new locations in central Asia.
Al Majalla correspondent Mahmoud Khalil, who conducted the interviews, told AP he received an e-mail two months ago from the man purporting to be bin Qais, saying he was the new spokesman and was using a list of contacts maintained by his predecessor, Abdel Rahman al-Rashed.
Khalil said he was suspicious until bin Qais reminded him of a private exchange between him and al-Rashed about an interview he was trying to arrange with an al Qaeda operative.
Khalil said bin Qais gave no information on his own background but claimed he took the job of media contact as part of al Qaeda's restructuring, which followed the international crackdown after the Sept. 11 attacks.
In a message received Tuesday, bin Qais warned of plots "the size of the Sept. 11 attacks" being devised against the United States. "A strike against America is definitely coming," he said.
Bin Qais said the arrests of key al Qaeda figures, including suspected Sept. 11 mastermind Khalid Sheikh Mohammed, would have little effect on the organization because old timers had been replaced by newcomers "who have a very good security cover."
A recent State Department report estimates al Qaeda's strength at several thousand members.
The group "has cells worldwide and is reinforced by its ties to Sunni extremist networks," the report notes. Since the war in Afghanistan in 2001, it "has dispersed in small groups across South Asia, Southeast Asia, and the Middle East and probably will attempt to carry out future attacks against U.S. interests."
One of the questions about al Qaeda is how much of its leadership remains intact, especially whether bin Laden is alive. Since U.S. forces believed they had bin Laden pinned down in caves in Afghanistan's Tora Bora mountains in December 2001, only partial evidence that he is alive has emerged, in the form of taped messages purportedly featuring the voice of the al Qaeda leader.
The most recent ones condemned the U.S. campaign Iraq, calling on Iraqis to resist the invasion. The statement deplored the secular regime of Saddam Hussein, but said the presence of American troops was a more important issue.
Worries that the U.S. invasion would trigger an attack at home led the Department of Homeland Security to increase the national terror alert in the first days of the war. It was reduced from "high" back to "elevated" last month as the fighting in Iraq abated.