FALLING INTO LIFE: Essays by Leonard Kriegel (North Point Press: $19.95; 210 pp.). Recounting how the author lost the use of his legs as a child during a national polio epidemic and then staked his claim "as an American who had turned incapacity into capacity," these essays offer as powerful a paean to human potential as the classic work on rising above disability, Henry Viscardi Jr.'s "A Man's Stature" (1952). "Falling Into Life" is nevertheless a far more radical work, for while Viscardi was preoccupied with living up to social conventions, as was his era, literature professor Leonard Kriegel tries to transcend them. For instance, while he celebrates his courage while learning to walk--being "suspended in air when nothing stood between me and the vacuum of the world"--he also acknowledges, after falling one too many times, that there is wisdom in "facing the question of endings." Kriegel's essays can be powerful literature, as when he compares his repeated immersions in a hot pool to baptism--his "wafer" a salt tablet intended to combat dehydration. But Kriegel is most striking as a polemicist, assailing such modern euphemisms as "disabled," for instance, for having denied him "the rage, anger and pride of having managed to survive as a cripple in America."