Australian satirist Jolley (introduced to American readers last year with Miss Peabody's Inheritance and Mr. Scobie's Riddle) lays her third novel at a fat farm, where along with the diet of carrots and lettuce, a motley collection of human dumplings divert their attentions from their panging tummies by taking courses in the fine arts. Jolley gets a chance to roast avocational critics (""Bear in mind the Freudian slip and the Freudian construction and for heaven's sake don't lose sight of the Oedipus and the Electra complexes. . .""), canting wine connoisseurs, aging actresses writing awful autobiographies, and many more. All, alas, are too-easy targets for satire, but the book, nevertheless, summons smiles and the occasional chortle. To Trinity College (site of the fat farm) comes the unassuming spinster-novelist Alma Porch, armed with her film treatment, ""Foxybaby,"" which she plans to put to rock music, stage and videotape. Headmistress Josephine Peycroft--flamboyant lesbian and dilettante--has an agenda of her own, including casting rich fat-farm ""angel"" Mrs. Viggars as the lead (albeit the role calls for a 60-year-old man) and setting the ""Foxybaby"" story to cello and mime. On top of this, Alma must cope with chatty roomie Jonquil Castle (a sad but stupid elderly lady whose every utterance is of her grandchildren), with the advances of all the sex-starved dieters of every erotic persuasion (no trick for uptight Alma), and with the lack of her only means out of the chaos at Trinity--her trusty but wrecked VW. Turns out, along with their love of floppy hats and bright colors, all the fatties have hearts of gold and get enmeshed in Alma's new work-in-progress about a man caring for his drug-riddled daughter and her mewling infant. When Alma finally flees the farm, it's only to return, in a novelistic sleight of hand indicating all that's passed in the pages of the book has been a hallucination or dream. Jolley tries hard to amuse, but mostly prattles. Actually, the vividness and intensity of the ""Foxybaby"" treatment within the novel (satirically intended though it may be) makes a reader wish that Jolley would step off the broadly comic boards she's trod in three books now, and move on to something more substantial.