Has the United States government ever censored nudity in works of art?
The United States has considered this in a law. Wikipedia states that the United States has an obscenity law which governs whether the work of art is obscene or not, and thereby determining whether it must be censored.
Nudity is censored on public TV because children don't need exposure to the sight of naked bodies! Censoring TV nudity ensures that children only get to see programs and content suitable for all ages. Usually programs containing nudity are restricted to a 'watershed' time - for example 9pm - when most younger children are normally in bed.