Insurgents in Afghanistan, fighting from some of the poorest and most remote regions on earth, have managed for years to maintain an intensive guerrilla war against materially superior American and Afghan forces. Weapons from a police post linked to an attack on Americans. Most rifles were the kind issued by the United States. Arms and ordnance collected from dead insurgents hint at one possible reason: Of 30 rifle magazines recently taken from insurgents corpses, at least 17 contained cartridges, or rounds, identical to ammunition the United States had provided to Afghan government forces, according to an examination of ammunition markings by The New York Times and interviews with American officers and arms dealers. The presence of this ammunition among the dead in the Korangal Valley, an area of often fierce fighting near Afghanistans border with Pakistan, strongly suggests that munitions procured by the Pentagon have leaked from Afghan forces for use against American troops. The scope of that diversion remains unknown, and the 30 magazines represented a single sampling of fewer than 1,000 cartridges. But military officials, arms analysts and dealers say it points to a worrisome possibility: With only spotty American and Afghan controls on the vast inventory of weapons and ammunition sent into Afghanistan during an eight-year conflict, poor discipline and outright corruption among Afghan forces may have helped insurgents stay supplied.