The Farnesina in Rome is Italy's national gallery of drawings. The works of Leonardo, Raphael and Tintoretto, among others, are displayed there. Now, for the first time, there is a show by a living artist displayed there. Robert Baxter is the artist and he is also the first American to show in the gallery. The Milwaukee native has been living in Rome for 10 years and he explained his expatriation: "Being a painter here is respectable in a way it isn't in the United States. Here if you say 'I'm a painter,' any charwoman or man who collects tickets on the bus knows immediately what you mean. In the United States, you're looked on as a sexual deviate or a guy with a bomb under his trenchcoat." . . . Earlier this week Armand Hammer, industrialist and art collector, was made an honorary citizen of Vinci, a Tuscan town not far from Florence. Vinci is the birthplace of Leonardo da Vinci, and Hammer made headlines 14 months ago when he paid $5.8 million at auction for Leonardo's notebook "The Leicester Codex," a treatise on hydrodynamics written backward in mirror writing. He has also included a provision in his will that the Codex be shown in Florence at least once every five years after his death.