Afghan Region's Politics Snarl U.S. War Plan
Goals set by Pres Bush to root out Al Qaeda terrorists and Afghanistan's Taliban government become deeply entangled in murky politics that have kept Afghans fighting for more than 20 years; decision not to bomb Taliban front lines at point where breakdown would leave Kabul open to immediate capture by opposition Northern Alliance reflects grim strategic reality: Pakistan, crucial ally for US in meeting Bush's war aims, has threatened to close its airspace to American aircraft and cancel support if bombing allows Northern Alliance to overrun Kabul; Pakistan regards Northern Alliance, which has been supported by Iran and Russia, with deep suspicion; Gen Pervez Musharraf, Pakistan's president, claims he has ironclad understanding with Washington that Northern Alliance will not be allowed to 'draw mileage' from American bombing by closing in on Kabul before arrangements are complete for new government that will be friendly to Pakistan, as Taliban has been; as result, US military strategy could become hostage to bitter enmities that have long bedeviled Afghan politics, allowing Taliban to consolidate its position; photos (M)