The latest Inspector Morse yarn from the redoubtable Dexter (The Way Through the Wood, etc.) might well be subtitled ""Morse Meets C.P. Snow,"" because part of the plot-about the machinations at an Oxford college to succeed the retiring Master-owes a good deal to Snow's The Masters (Morse even mentions the book in his one-uppish way). There is, however, more than academic politics to this tale involving two murders on a quiet Oxford suburban street, one of which was apparently a case of mistaken identity, and an alibi created with truly fiendish ingenuity. As usual with a Morse mystery, the Inspector's offbeat personality and his odd relationship with his earnestly lowbrow sidekick, Sergeant Lewis, provide much of the pleasure; the plot is entirely workmanlike. Here Morse, who seems to be drinking more than ever, has a nasty diabetic episode, slows down for a while, has a gratifying flirtation that actually ends up in bed and is ultimately forced to pen a touching missive to Lewis that reveals, in that stiff-upper-lip British way, a degree of affection for the man. A treat for buffs, this is also a good introduction for newcomers to an addictive detective. Author tour. (Mar.) FYI: In March and April, PBS will air new Morse episodes on Mystery! During 1997, Ivy Books will reissue five Inspector Morse novels in paper.