By GINIA BELLAFANTE

Thet've given us renaissance painting; we've thanked them with Kraft American Singles. Now the Italian-American cultural exchange will be offset again. Italy's latest export: the brilliantly funny actor-director ROBERTO BENIGNI, 39. His smash hit Mafia comedy, Johnny Stecchino, is currently opening Stateside. Next year he will star in an American farce, Son of Pink Panther. That project, says Benigni with boyish delight, "is the most wonderful thing I've done."