A major reorganization of allied forces in Afghanistan will centralize both American and other foreign troops under the direct command of Gen. Stanley McChrystal, the senior U.S. and NATO commander in the theater.

The move, which will further boost McChrystal''s authority, came as his boss, Gen. David Petraeus, predicted 2010 will be a difficult year and that the fighting in Afghanistan will "likely get harder before it gets easier." He told the U.S. Senate Armed Services Committee he expects American forces to reverse the momentum gained by the Taliban.

Vice Adm. Greg Smith, the top military spokesman in Afghanistan, said the reorganization would integrate most of the 20,000 U.S. troops currently serving in the eastern part of the country under separate command, known as Operation Enduring Freedom, into the 100,000-strong NATO-led International Security Assistance Force.

NATO officials stressed that this will create a streamlined and simplified command structure, since both forces already are under McChrystal''s operational control.