Suppose the tragic old man raging amid the storm is not on a heath but in a cornfield. Suppose that he is not an ancient British king named Lear but a prosperous Iowa farmer named Laurence Cook, and that his daughters are not Cordelia, Regan, and Goneril, but Caroline, Rose, and Ginny. Then suppose that what he suddenly suggests dividing among them is not his kingdom but his vast acreage of prime farmland. Before you say that it sounds pretty corny, consider what a plot lifted from the well-known Stratford playwright can become in the hands of a subtle and intelligent thief. The Russian novelist Ivan Turgenev wrote a fine, bitter novella called A Lear of the Steppes, and now Jane Smiley has written a fine, bitter, baffled, suspenseful novel that could as easily be called A Lear of the Plains. One thing that saves A Thousand Acres from being a schematic recasting of Shakespeare's play is that the plains themselves share center stage with the tragic family fighting over a piece of them. The perfect flatness, as awe-inspiring as it is monotonous, the stunning heat and numbing cold, the dust and mud that defeat the most vigilant farm woman's efforts to keep them out of the house, the storms gathering on the horizon, the marshes and flooded quarries where the surface of the earth dipped below the surface of the sea within it all are as precisely evoked as the clothes, food, manners, and intimate feelings of the hardworking farm people who have lived with them for generations.Above all, Smiley's formidable, stoical, laconic Lear, Laurence Cook, however abysmal his dark side the novel is a bit overladen with dark sides, retains his tragic stature. In his adamant narrowness his fatalistic motto is what you get is what you deserve he makes the other characters seem shallow and temporizing, and his daughter remains in awe of the man she has repudiated: ''Perhaps there is a distance that is the optimum distance for seeing one's father, farther than across the supper table or across the room, somewhere in the middle distance: he is dwarfed by trees or the sweep of a hill, but his features are still visible. Well, that is a distance I never found. He was never dwarfed by the landscape the fields, the buildings, the white pine windbreak were as much my father as if he had grown them and shed them like a husk.'' Even with an anticlimactic ending in place of the original's wrenching close, Smiley has succeeded in transplanting something of Lear's mythic power to the bleak American plains. Another thing is that Smiley engineers a deft turning of the tables. Ginny is the narrator, so we get Goneril's version and a Lear who is more wrong than wronged. The story is really about the transformation of Ginny, through painfully earned knowledge, from a compliant, trouble-suppressing, guilt- ridden daughter and wife into an angry though still ambivalent independent woman who has to cast off the only kind of life she has known. The crucial role played by a neighbor's returned prodigal son, who has been converted to vegetarianism and organic farming, puts ecological as well as feminist issues on the table that Smiley has turned, though she has too much respect for her characters to make them figures in a tract.