When three-month-old Lia Lee arrived at the county hospital emergency room in Merced, California, a chain of events was set in motion from which neither she nor her parents, Foua and Nao Kao, were part of a large Hmong community in Merced, refugees from the CIA-run ''Quiet War'' in Laos. The Hmong, traditionally a close-knit and fiercely independent people, have been less amenable to assimilation than most immigrants, adhering steadfastly to the rituals and beliefs of their ancestors. Lia's pediatricians, Neil Ernst and his wife, Peggy Philip, cleaved just as strongly to another tradition: that of Western medicine. When Lia Lee entered the American medical system, diagnosed as an epileptic, her story became a tragic case history of cultural miscommunication.