"If someone is determined, and has the right access, they could do damage that would affect thousands of lives," Sweet said.
Al Qaeda has already put out the word in its online magazine, Inspire, for "brothers of ours who have specialized expertise and those who work in sensitive locations that would offer them unique opportunities to wreak havoc on the enemies of Allah."
As evidence of American infrastructure vulnerabilities, the report specifically cites the attempted insider sabotage this April at a water treatment plant in Arizona.
Officials said then a disgruntled night shift worker took over the control room and tried to create a giant methane gas explosion.
"I am taking the plant hostage," the worker said in a recorded 911 call.
There was no tie to al Qaeda and his plot failed, but the incident was a reminder of how easily one insider could create potentially deadly mayhem.
"Facilities in the United States don't have to be attacked by terrorists with airplanes or bombs outside the facility," Clarke said.