THE SPECTATOR BIRD By Wallace Stegner (Penguin: $8.95) . The narrator of this National Book Award-winning novel, retired literary agent Joe Allston, describes himself as "just killing time until time gets around to killing me." Allston's search for the meaning of his existence takes him beyond the well-ordered comfort of his Northern California farm as he retraces a trip he and his wife made to Denmark years before. Wallace Stegner deftly interweaves the story of their efforts to recover from their son's suicide with a darker tale involving the lovely, ruined countess they befriend. Reliving this double tragedy enables Allston to rediscover his commitment to his patient wife and bid farewell to the life he might have led.