Lack of Rules Cited in Death Of Schoolgirl; Bus That She Rode On Faced Less Regulation
School bus that struck and killed Juhi Shah moments after dropping her off in front of her Queens home is owned and operated by Aucar's Transportation, private bus company that is not subject to stringent safety regulations for public school bus services; death of Shah, kindergartner at Our Lady of Mercy Roman Catholic School in Forest Hills, has prompted number of state and local investigations; Auden Cardenas, company's owner, was driving bus; Shah photo (M)