PUBLIC funding of the arts is one of those subjects, like abortion funding and the status of women in America, about which reasoned discourse is rapidly becoming impossible. Not long ago President Carter was reported as complaining that he had been compelled to devote more time to considering his appointments to head the National Endowments for the Arts and Humanities (Livingston L. Biddle and Joseph Duffey, respectively) than to the SALT talks. With all the fervor of an Eleanor Roosevelt, Joan Mondale has taken up the banner of the Arts, and so has been dubbed Joan of Art. She appreciates the arts almost every minute of the day, she has let it be known, and one could wish her an honest Philistine to grapple with. Alas, none is in sight, only a "fiscal crisis."