Manhattanites frequent this ristorante as much for the winning enthusiasm of owner/cookbook author/Public Television chef Lidia Bastianich as for the food. The menu emphasizes authentic regional Italian cuisines, with a bow to dishes from Bastianich's homeland, Istria, on the Adriatic. Sit in an attractive front room with a wooden bar, a rustic room beyond, or in the elegant second-floor dining room. Order risotto, fresh homemade pasta, or roasted whole fish, and choose from a wine list representing Italy's finest vineyards. Reservations essential. Jacket required. Subway: N, R, W, 4, 5, 6 to 59th St.-Lexington Ave.