This is a good time for a novel sabotaging fundamentalism. Reading the news, you get the impression that Allah forbids pork but heartily endorses truck bombs and that Paul commended semiautomatic weapons to the Corinthians. ''Mentus means 'mind,''' one of the scholarly heroes of Wilton Barnhardt's Gospel says to a TV evangelist. ''Fundus to the Romans meant 'anus.' Fundamentalist: a mind like an anus.''
This is mischievous scholarship; most of Gospel is scholarly mischief. It's a crowded, colossal fictional St. Peter's for lapsed Catholics or liberal Catholics and agnostics who think religion is a racket but who have to admit that life would be much less interesting without it.
The plot is generated by a quest for a mysterious fifth Gospel, a scroll that outscrolls even the Dead Sea Scrolls. As in most fictional quests, the object matters less than the obstacles along the way. It begins when Lucy Dantan, a 28-year-old theology student at the University of Chicago, is sent to England to retrieve Patrick O'Hanrahan, a renegade professor who has disappeared in a cloud of credit-card bills charged to his department. She evolves from a fly in his ointment to a sidekick as the elusive scroll takes them from Oxford to Ireland, Italy, Egypt, Jerusalem, and born-again Louisiana.
Lucy's residual faith is imperiled by her meeting a Greek Adonis, handsome as a statue and about as smart, and by O'Hanrahan's course of lectures. Christian Follies and Frauds 101: doctored Scriptures, faked relics, and papal orgies. The reader also gets the sought-after Gospel, written by Matthias, a disciple who found his faith by losing it. Barnhardt doesn't bother to make it sound anything but apocryphal, but it's based on solid scholarship. What Paul, inventing Christian orthodoxy, took out of its confused, sectarian Jewish context is put back in. Yet the voice of the Trinity, which has gotten a parenthetical word in edgewise throughout the novel, gets the last word: The only faith that counts is good works. Barnhardt has written an impish but not exactly impious book. It is a dialogue with Rabelais' ''Great Perhaps,'' a comic catechism for doubting Thomases. A