Washington (CNN) -- The rash of attempted homegrown terrorist attacks over the past year has the counterterrorism community working at a "relentless" pace to deal with the challenges posed by an evolving enemy, according to the nation's chief counterterrorism officer.
Michael Leiter, director of the National Counterterrorism Center said Wednesday that "the pace has been relatively frenetic since 2001, and I can tell you that the past 13 months have been as intense if not more intense because of the variety of threats in any time since 2001."
In a presentation at a Washington think tank, Leiter said the face of terrorism has evolved over the past dozen years from being centered on al Qaeda central, to the rise of affiliate groups to the current phase where those affiliates have become self sustaining, independent terrorist organizations.
Leiter indicated these groups, such as al Qaeda in the Arabian Peninsula, still have "tentacles back to al Qaeda leadership" in Pakistan, but their independence makes it far more difficult for the intelligence community.
"They operate at a different pace and with a different level of complexity than does al Qaeda senior leadership, and that has complicated our task significantly," Leiter said.
The Yemeni-based AQAP has been linked to a number of terrorist plots against the U.S. including the failed attempt last Christmas to blow up a Northwest Airlines international flight into Detroit, Michigan, and the recently discovered cargo bomb plot.
One of AQAP's operational leaders is Anwar al-Awlaki, a U.S.-born cleric who now resides in Yemen and has been linked to Umar Farouk AbdulMutallab, the suspect in the Chirstmas Day bombing attempt, and U.S. Army Maj. Nidal Hasan, who is accused of killing 13 people during a shooting spree at Fort Hood, Texas, last year.
Leiter took exception to suggestions that luck was behind the failure of some of the homeland plots.
Although acknowledging the performance of the counterterrorism community has not been perfect, Leiter said the successes are the result of hard work.
"Of course luck does play a part in some of these things," he said, "but in many cases -- and this is what many in the public do not see -- the counterterrorism community helps make its own luck."
Leiter said the threat of a severe, catastrophic attack against the U.S. has significantly diminished as well as the likelihood of a chemical, biological or radiological attack. But neither has been eliminated as a possibility.
Leiter said a key to battling the terrorists is for the United States to be resilient, to not think of them as being all-powerful.
"We should not assume that the terrorists are 10 feet tall. It turns out that in an open society with millions and millions of people crossing our borders every day, with the tools of a terrorist being readily available in many ways whether or not it's firearms or precursors for explosive devices, we shouldn't assume that they're 10 feet tall," he said. "We have to be taller than them. We have to be more resilient than them."The counterterrorism chief also suggested the need to move away from the rhetoric of clash of civilizations because it feeds into the al Qaeda discourse that they are defending Muslims against the West. "It's easy to show the futility of al Qaeda's message," he said.
One thing Leiter would like to see changed: less talk about al Qaeda.
"It is not always best for us to hammer the counterterrorism drum over and over again, because by doing so we can in fact glorify al Qaeda, who are simply a bunch of murderous thugs."