Among the key findings of the classified estimate, which is still in draft form and must be approved by all 16 U.S. spy agencies:

—The U.S. will face "a persistent and evolving terrorist threat" within its borders over the next three years. The main danger comes from Islamic terrorist groups, especially al-Qaida, and is "driven by the undiminished intent to attack the homeland and a continued effort by terrorist groups to adapt and improve their capabilities."

—Al-Qaida is probably still pursuing chemical, biological or nuclear weapons and would use them if its operatives developed sufficient capability.

—The terror group has been able to restore three of the four key tools it would need to launch an attack on U.S. soil: a safe haven in Pakistan's tribal areas, operational lieutenants and senior leaders. It could not immediately be learned what the missing fourth element is.

—The group will bolster its efforts to position operatives inside U.S. borders. In public statements, U.S. officials have expressed concern about the ease with which people can enter the United States through Europe because of a program that allows most Europeans to enter without visas.