The temptation to play God is an occupational hazard for science fiction writers. A case in point: the richly imagined, consistently engaging and self-destructively ambitious EARTHLING, by Tony Daniel. The novel opens with a stylistic tour de force in which apparently random entries in a geologist's field journal coalesce into the memories of a dead man that have been downloaded into the electronic brain of a mining robot. Although the robot has access to these sophisticated memories, its own awakening consciousness is appropriately childlike. Designed to bore through the earth's crust and mantle to the core of the planet, the robot patiently endures years of abandonment as its human creators fall victim to a social convulsion that changes the face of the land as well as the structure of civilization. By the time the robot has achieved a semblance of maturity, it has learned to think for itself, to read (Jane Austen's ''Emma'' is a favorite) and to feel: ''The robot feels one of the legs'' of its mobile unit ''jerk spasmodically. Then the other jerks, without the robot wishing it to do so. The robot . . . jitters and shakes for a long time. This is the way the robot cries.'' This is dazzling stuff. But just when we have become intimate with the robot -- who has acquired a gender (male) and the name Orf (short for Orpheus) -- the focus suddenly shifts. We are still on the Olympic Peninsula in the Pacific Northwest, but years have passed, political authority has splintered among antagonistic ''tribal'' units, and we are now inside the head of Jarrod, a ranger of the fiercely independent Park Service whose single-minded dedication to protecting the trees of the Olympic National Forest leaves no room for the joys and burdens of human reproduction. After an initial reluctance to leave Orf the robot behind, I was enthralled by Daniel's account of Jarrod's journey of self-discovery through a much-altered Western America. But my pleasure was tempered by a sense that the larger narrative was veering out of control. Far below the earth's surface, Orf has encountered godlike beings, who begin to play a larger and larger role in the story. Whenever the spotlight falls on these deities, the novel's otherwise precise language turns fuzzy. They are described as ''sentient ecologies'' and ''immensely complex children,'' and they inspire writing like this: ''It's a long trip to the stars and the way lies through beauty. . . . You walk the beauty lines, the traceries of pattern and purpose that are folded and dimpled into reality as surely as are gravity wells and electromagnetic fields.'' As New Age reveries go, this is better than most. But by the emphatically uplifting conclusion, I found myself longing for the literally down-to-earth voice of the earlier Orf, whose relief when Jane Austen's Emma finally realizes that she loves Knightley is expressed in these carefully clunky terms: ''It is as if some clogged line in the robot's hydraulics had a sudden release of pressure or rock that had long been hard and tough became easy to move through.''
