''Oracle Night'' is the title of a novel within a pointedly abandoned novel within this wholly self-parodic novel. After Sidney Orr, a middle-aged writer getting back to his work after a near-fatal illness, buys a Portuguese notebook from a Chinese shopkeeper, the floodgates of his imagination open, and fine prose flows forth. ''Be careful, Sid,'' a friend warns, of this magical stationery. ''You have to watch out that you don't get lost.'' Anyone familiar with Auster's old books -- his spare yarns of vanishing and chance -- can guess that Sidney's fiction will bleed into his reality. His chilling ghostliness, however, has been supplanted by insulting mystic hoo-ha and his smooth plot work replaced by garish leaps and twists.