Last week members of a Marine reconnaissance patrol told of a skirmish fought with an enemy unit near the town of Phu Bai.  Among the Viet Cong killed was the apparent leader of the guerrilla band—a slender young Caucasian with long brown hair.
    The young white was wearing a shabby green uniform with a red sash tied across the chest.  In his hands was an AK-47, the Soviet-designed automatic weapon used by North Vietnamese regulars.
    The Marines are convinced that the guerilla leader was an American, a Marine enlisted man who has been carried as missing in action since 1965.
    In the past few months, they add, they have received a number of reports of Americans operating with Viet Cong units in the Phu Bai area.