When Mrs. Hollingsworth, a spirited, eccentric lady, first encounters the truculent 12-year-old boy whose seduction of her (unless it's the other way around) is the subject of ''Trick or Treat,'' the opening story in Padgett Powell's new collection, she is thinking, as Powell's characters so often do, about the South. ''The South?'' challenges the boy, a leering ''portrait of insolence.'' ''What's that?''

'' 'This,' Mrs. Hollingsworth said, indicating with her arm the trees and air and houses and suspiring history and ennui and corruption and meanness and game violators and bottomland and chivalric humanism and people who are smart about money and people who don't have a clue and heroism and stray pets around them.''

She might have added to this list writers who populate their fiction with spirited eccentrics and who write in great rushes of lyricism, testing the conventions of syntax or flouting them outright. For superimposed upon the actual South, at times blotting it out entirely, is an imaginary region of unsurpassed fertility, whose history suspires largely in books. We are at present in the midst of yet another quiet boom in Southern fiction, as writers like Larry Brown, Lewis Nordan, Jill McCorkle and Frederick Barthelme politely jostle for space in the pantheon alongside William Faulkner, Flannery O'Connor, Robert Penn Warren and Walker Percy.