If television educates the masses, then PBS is the national university. In making an effort to be sober and comprehensive even at the risk of dullness (the productions of Ken Burns being a case in point), the network is always trying to improve our minds. With "Culture Shock," a new four-part series whose first two parts air tonight, PBS's role as national schoolmarm takes on a further dimension.

"Culture Shock" tells us that today's various flaps and fusses over violence in the movies, weirdness in the art galleries and nastiness in song lyrics are an old and repetitive story. It could be summed up with old saws like "There's nothing new under the sun" or "The more things change, the more they stay the same." Which begs the obvious question: Why remind us? Don't we know that people thought impressionist art was scandalous in the late 19th century? Don't we have some sense that people always had problems with "Huckleberry Finn"?

The four installments (I've watched three) are unevenly inventive, but at their best they are thoughtful and even entertaining. The strongest is the opening 90-minute piece (tonight at 9 on Channel 26, followed by the 60-minute Part 2 at 10:30) about "The Adventures of Huckleberry Finn," which was published in 1885 and almost immediately banned from a library in Massachusetts for being coarse and lacking in intellectual nobility. The film weaves together literary and social history and contemporary protest, along with reassuring and intelligent commentary from several academics. There is also a sly look at modern-day Hannibal, Mo., which has turned into a Twain theme park, appalling and yet so very plastic-American.

Three of these commentators are black, a conspicuous choice given that the main reasons people have objected to the use of the book in high schools is its depiction of the runaway slave Jim and the use of the N-word. The three elucidate the text very effectively--especially David Bradley, a writer and Twain expert who explains some of the subtleties in the novel as well as the time in which it was written.

The objectors are represented by a mother in Tempe, Ariz., Kathy Monteiro, and her daughter Raquel Panton. Both are also articulate and intelligent, but as the film follows their efforts to have the book removed from the high school curriculum they begin to seem a bit hysterical about it. No one can avoid hurt, says Bradley.

However, they raise important questions that the film doesn't really answer: Is the book really so luminously great that teenagers should be required to read it, with its minstrelish portrayal of Jim and 200-plus mentions of a deeply denigrating word, especially if their teacher has not had the benefit of special training to present it in proper context? Clearly some readers--whatever their age--are going to read it and get it, particularly if they've seen the cram course provided by this program. But I was not convinced that the book is so stupendous it should be essential reading for everyone.

The unanswered question in Part 3, "Hollywood Censored: Movies, Morality and the Production Code," airing next Wednesday, is posed by Robert Peters, president of Morality in Media (I don't know what that group is; it sounds ominous). Why is it, he asks, that some of the best films Hollywood ever made were produced during the 30 years that there was no profanity in movies, thanks to a censorship code that is now almost universally decried? It does make you wonder.

The movie segment is basically a history of the production code from its start after Hollywood's murder, sex and drug scandals of the 1920s. First a Presbyterian minister with really bad teeth named Will Hays was hired by the movie moguls. His job was to convince the public that the studios were adhering to a code that banned certain words (including "fanny," "slut" and "goose") and required that murders be presented in such a way as not to inspire imitation. It turned out the studios had no intention of following this code because they wanted to make movies that would sell tickets.

By the early 1930s the Catholic Church, Protestants and Jews all joined to boycott movies they found morally repulsive, and from that alliance the infamous Joseph Breen was hired to enforce the code and what one commentator calls a Roman Catholic morality, with the authority to enforce $25,000 fines for noncompliance. Some of the best footage in this segment is of Breen lecturing and describing what was wanted from Hollywood. What this country needs is not a five-cent cigar but clean, rollicking comedy, he declared.

Tonight's second segment is about Edouard Manet's painting "Olympia." This is basically an art history lecture, which is certainly fun and interesting, but it fails to make the contemporary connection of the other programs. (The fourth program, "The Devil's Music," also airing next week, is about 1920s jazz.) We learn, from a series of critics and art historians who all have noticeably impeccable French accents, that the picture caused a scandale not because it was a lubricious nude but because its subject was a courtesan, provoking class and gender consternation.

The underlying message of the series is that great art makes waves. Any great writer is constantly trying to cause trouble, says David Bradley in the Twain episode. That trouble may be intentional or it may be accidental, but it is always valuable. What the series does not--perhaps cannot--tackle is the question of what to do about all the bad art that causes trouble.

CAPTION: Osgood Perkins, Karen Morley and Paul Muni in "Scarface," a 1932 film whose violence helped pave the way for the Hays Code.

CAPTION: Catholics campaign for "decent movies" in the early 1930s.