In a shift with profound implications, the Bush administration is attempting to re-energize its terrorism-fighting war efforts in Afghanistan, the original target of a post-Sept. 11 offensive. The US also is refocusing on Pakistan, where a regenerating al-Qaida is posing fresh threats. There is growing recognition that the United States risks further setbacks, if not deepening conflict or even defeat, in Afghanistan, and that success in that country hinges on stopping Pakistan from descending into disorder. Privately, some senior US military commanders say Pakistan's tribal areas are at the center of the fight against Islamic extremism; more so than Iraq, or even Afghanistan. These areas border on eastern Afghanistan and provide haven for al-Qaida and Taliban fighters to regroup, rearm and reorganize. This view may explain, at least in part, the administration's increasingly public expressions of concern.