OLD GRINGO <i> by Carlos Fuentes (Harper & Row: $7.95)</i>

In this shimmering, challenging novel, Carlos Fuentes brings together three oddly matched characters, united by a longing for fulfillment: a Mexican revolutionary general in the service of Pancho Villa, a prim, frustrated teacher from Washington, D. C., and writer Ambrose Bierce (who rode into the Mexican wilderness in 1914, never to be seen again). Fuentes uses the interaction of this trio as a vehicle for a series of convoluted internal monologues. He considers the origins of revolution, the nature of commitment, the search for love and the conflict between human aspirations and achievements. The result is both a fascinating work of fiction and an insightful meditation on the conflicts between Hispanic and Anglo cultures. It’s not clear why Fuentes chose Bierce as the man who fears nothing because he is weary of living: He burdens the character with a mawkish sentimentality that would have infuriated the author of “The Devil’s Dictionary.”