But the report continues that "US recruits are hard to find and al-Qa'ida detainees have reported that US citizens can be difficult to work with, one senior detainee claimed that US citizens and others who grew up in the West, were too independent and thought they knew more about US operations than senior planners."
In addition, women and married couples with children are being actively recruited, according to the report.
"A senior al-Qa'ida detainee instructed an operative who is currently in US custody, to settle in the United States with his family and maintain a low profile before eventually conducting an attack," the report reads. "Al-Qa'ida operatives have also married US women to obtain US visas and foreign documentation from other countries, according to sensitive reporting."
The FBI says it takes no solace in the lack of evidence, or about what it is not seeing.
"Individual operatives who possess a clean passport, have not come to the attention of intelligence agencies overseas, and lack a criminal record are unlikely to attract the attention of security agencies in the United States, unless they are in contact with known extremists," according to the report. "Al-Qa'ida has altered its operative profile, making it more difficult to screen visa applicants at embassies and individuals entering the United States at airports and other border crossings."
And the report suggests that instead of actual sleeper agents, lying in wait, al Qaeda may rely on disaffected Americans or other sympathizers, who might pick easier, softer targets such as shopping malls.
Clarke warned, "We have reason to believe that techniques like that and others we shouldn't talk about are well known to terrorists around the world."
ABC News' David Scott contributed to this report.