Washington (CNN) -- Nearly nine years after the September 11, 2001, terror attacks, Americans still face a serious threat from al Qaeda, but the nature of the threat has changed, according to a new report from a panel of top national security experts.
The 42-page analysis warns of the growing threat of homegrown terrorism and the role played by U.S. citizens and residents within al Qaeda and allied organizations. It describes an increasingly wide range of "U.S.-based jihadist militants" who do not fit "any particular ethnic, economic, educational, or social profile."
The report was produced by the non-partisan National Security Preparedness Group, chaired by former Rep. Lee Hamilton, D-Indiana, and former Gov. Tom Kean, R-New Jersey, who also headed the 9/11 commission.
The United States, the report asserts, now confronts "a dynamic threat that has diversified to a broad array of different attacks, from shootings to car bombs to simultaneous suicide attacks to attempted in-flight bombings of passenger aircraft."
Would-be terrorists are now likely to attempt more frequent and less sophisticated attacks with fewer casualties compared with what transpired in 2001, the report states.
Georgetown University Professor Bruce Hoffman, who helped prepare the study, said the attacks are not individual, isolated events. "Rather, we see them as part of a broader strategy embraced by our adversaries -- by al Qaeda, its affiliates and associates -- to flood us, in essence, with multiple threats from a diverse array of adversaries," he said.
The report said preventing such attacks will require greater involvement from state and local public safety officials.
Stephen Flynn, a National Security Preparedness Group member, told reporters at a news conference Friday that the smaller-scale attacks using domestic recruits are much harder to detect and intercept. "As a practical matter, it means that we will almost certainly have successful terrorist attacks on U.S. soil and we need to start coming to grips with that," Flynn said.
Hoffman said that terrorists might "have found our Achilles' heel" because "there is no single goverment agency responsible for identifying radicalization and interdicting recruitment" in the United States.
The report makes no recommendations. The National Security Preparedness Group decided it would focus this report on studying the evolving threat and take a few additional months to prepare recommendations for policymakers.
"Al Qaeda or its allies continue to have the capacity to kill dozens, or even hundreds of Americans, in a single attack," the report concludes. And al Qaeda leaders still "hope to inflict mass casualty attacks in the United States."
While the threat now is less severe "than the catastrophic proportions of a 9/11-like attack, (it) is more complex and more diverse than at any time over the past nine years."
The report, drafted by Hoffman and Peter Bergen -- who also is CNN's national security analyst -- states that al Qaeda's ideological influence has increased among other jihadist organizations in South Asia and in countries such as Somalia and Yemen.
"American overreactions to even unsuccessful terrorist attacks ... have arguably played into the hands of the jihadists," it asserts.
Al Qaeda and its allies have been hampered, the analysis says, by U.S. drone attacks in Pakistan and negative attitudes toward Islamic extremists in both Pakistan and the broader Muslim world.
CNN's Alan Silverleib and Pam Benson contributed to this report