By Phil Stewart WASHINGTON (Reuters) - Afghanistan troop casualties climbed 79 percent during key fighting months this year as the still-resistant Taliban kept up the pace of its attacks and NATO forces moved into a support role in preparation to end their combat mission, the Pentagon said on Friday. The data came in a Defense Department report to Congress that also showed NATO casualties falling 59 percent during the April-September period under review. The Pentagon did not provide the number of casualties for either year. Despite the jump in Afghan casualties and high attrition rates in the Afghan army, the report was broadly upbeat about the Afghan National Security Forces, or ANSF.