Is Liguria the next hot region of Italy? Certainly the last Tuscan cookbook has yet to be written, but Liguria is starting to get a fair amount of attention. Last year, Colman Andrews came out with the fine "Flavors of the Riviera: Discovering Real Mediterranean Cooking" (Bantam, 1986). Recently, Rizzoli released the photo-laden "Enchanted Liguria" ($40) by David Downie with pictures by Alison Harris. Now Fred Plotkin, author of the well-received "The Authentic Pasta Book" and other Italy-centered books, has written "Recipes From Paradise: Life and Food on the Italian Riviera" (Little, Brown; $32.50). None of these books are simply recipe books--the Ligurian people and seaside settings seem to inspire poetic pieces of writing. As for the food, this is a place where pesto is made in so many poetic variations that Plotkin is able to include 16 recipes for it.