Art and Politics Note: Vice-Premier Deng Xiaoping of the People's Republic of China originally was scheduled to open a major exhibition of American art March 26 in Peking but did not. The reason? According to reports out of China, hardliners in his Foreign Ministry advised against it on the grounds that it could be interpreted as a softening of China's position to U.S. arms sales to Taiwan . . .

Spaghetti Gangster-Flick Note: Sergio Leone, who created the Westerns that made Clint Eastwood a star, will direct Robert De Niro in a film called "Once Upon a Time in America." The film is not a sequel to Leone's "Once Upon a Time in the West," in which Henry Fonda played the villain . . .

Let's Not Face the Music Note: Some weeks ago this space reported that William Hurt would be playing "Richard II" in a unique production in New York. One that involved full frontal nudity (not Hurt) and staging the play in Celtic Britain, 1,200 years before the actual reign of the king. The press opening was postponed, at first because of the announced illness of director Marshall Mason, then last week Variety reported that there would be no official opening night at all because Mason decided it wouldn't please the critics . . .