WASHINGTON – Though mostly upbeat, the Obama administration’s assessment of war progress in Afghanistan suggests tough combat will continue for years and if the president begins to bring U.S. troops home next summer, as promised, the numbers will be small.

The internal review of President Barack Obama’s year-old war strategy unveiled Thursday says that Taliban momentum has been halted in many parts of Afghanistan and that al-Qaida leaders who are thought to be plotting further terrorist attacks on the U.S. from Pakistan sanctuaries have suffered grievous losses.

But the review makes clear that further progress won’t come easily. And it indicates that ultimate success depends heavily on factors beyond Obama’s control, such as Pakistan’s effectiveness in eliminating al-Qaida and Taliban havens on its side of the border.

Obama’s top national security aides insisted that while tough challenges remain, there is progress toward the goal of handing over control to the Afghan government by the end of 2014.

This year has been the deadliest in the war for U.S. forces. At least 480 American troops have been killed, compared to 317 last year and 155 in 2008.

Obama has stressed that the scale and pace of U.S. troop withdrawals starting in July 2011 depend on conditions on the ground.

Some allies, such as Canada, have already said they will end their combat mission next year regardless of how the war is going.

Obama cast the war as part of a broader effort to defeat al-Qaida, which is not present in Afghanistan in large numbers but has sanctuary in neighboring Pakistan.