WASHINGTON
-- Al-Qaida can be expected to attempt an attack on the United States in the next three to six months, senior U.S. intelligence officials told Congress Tuesday.

The terrorist organization is deploying operatives to the United States to carry out new attacks from inside the country, including "clean" recruits with a negligible trail of terrorist contacts, CIA Director Leon Panetta said. The chilling warning comes as Christmas Day airline attack suspect Umar Farouk Abdulmutullab is cooperating with federal investigators, a federal law enforcement official said Tuesday.

Al-Qaida is also inspiring homegrown extremists to trigger violence on their own, Panetta said.

The annual assessment of the nation's terror threats provided no startling new terror trends, but amplified growing concerns since the Christmas Day airline attack in Detroit that militants are growing harder to detect and moving more quickly in their plots.

"The biggest threat is not so much that we face an attack like 9/11. It is that al-Qaida is adapting its methods in ways that oftentimes make it difficult to detect," Panetta told the Senate Intelligence Committee.

Several senators tangled over whether suspected terrorists should be tried in civilian or military court. At the same time, a bipartisan group of lawmakers introduced legislation that would force the Obama administration to backtrack on its plans to try Sept. 11 defendants in federal court in New York and use military tribunals instead.

As al-Qaida presses new terror plots, it is increasingly relying on new recruits with minimal training and simple devices to carry out attacks, Panetta said as part of the terror assessment to Congress.