CENSORSHIP

''I have sworn upon the altar of God eternal hostility against every form of tyranny over the minds of men'' Thomas Jefferson (plaque over the entrance to new York Public Library exhibit, 'Censorship: 500 years of Conflict.')

Just short of a century ago, in March 1885, the trustees of the Concord, N.H. , Public Library voted to exclude from the shelves a book that they termed ''trash of the veriest sort.'' The offending work, one trustee said, '' deals with a series of adventures of a very low grade of morality; it is couched in the language of a rough dialect, and all through its pages there is a systematic use of bad grammar . . . The book is flippant and irreverent.''

The banned work: Mark Twain's ''The Adventures of Huckleberry Finn.''

Today, Twain's ''Huck'' would seem an unlikely subject for ostracizing. Or would it? Don't be too sure.

A just-opened show in the newly refurbished Gottesman Exhibition Hall of the New York Public Library (NYPL) speaks to this issue. It conveys the clear message that censorship has historically flourished in society as a result of fear of the new and innovative - that which challenges the established order. Examples abound - from the 15th- and 16th-century banning of the writings of Calvin, Luther, Machiavelli, and Rabelais to 20th-century book-burning by the Nazis, persecution of authors who advocated birth control and abortion, and recent attempts to exclude evolution from classroom texts and restrict the writings of government workers.

Vartan Gregorian, New York Public Library president, points out that over the centuries censorship has taken a variety of forms. For instance, Roman censors sought to determine who was suited for citizenship; religious censors held heresy to be an impediment to salvation; moral censors in the 19th century passed judgment on what was suitable for family reading and viewing; and governments still restrict the circulation of information in the name of national security, national dignity, and the stability of particular regimes.

Dr. Gregorian, in an interview, said that perhaps the most oppressive form of censorship is that which is self-inflicted - ''not forced by law but resulting from fear.''

''(Unfortunately) we have come to value security more than freedom, ambition more than virtue . . . and we're paying a high price for security,'' the prominent librarian insists.

The only real antidote, Dr. Gregorian said, is to open up thought through education - teach the dimensions of citizenship and the meaning of freedom. He refers to Richard Brinsley Sheridan's play, ''The Critic,'' in which one of the characters remarks that ''the number of those who undergo the fatigue of judging for themselves is very small.''

Gregorian says that libraries - through their collections and shows - provide the opportunity and means ''that will increase the precious number of those who judge for themselves.''

One of the principal aims of the censorship exhibit, explains its curator, Ann Ilan Alter, is to ''remind viewers that we have become complacent about freedom of expression.'' Miss Alter, who holds a doctorate in European history, points out that censorship appears in any society which is ''in conflict.'' She adds that the NYPL exhibit explains how ''censorship conflicts of the past plug into the censorship conflicts of today.''

Displayed are nearly 300 printed works and images that have been censored in the West during the past five centuries. ''The exhibition,'' Miss Alter indicates in the show's catalog, ''demonstrates the power of ideas to survive.''

She continues: ''At the heart of the exhibition lie the works themselves, the books, pamphlets, newspapers, broadsides, and prints. They are survivors, sometimes torn or mutilated, of the war of conflicting ideas and ideals.

For example, John Milton's ''Areopagitica,'' with its advocacy of a free press, is in the exhibition, as is a copy of Luther's German translation of the Bible - which, Miss Alter explained, helped spread ideas that changed the political and spiritual face of Europe and North America. Also on display are copies of the Roman Catholic Index of Prohibited Books as well as some of the volumes it tried to suppress. Visitors can examine scores of polemical and satirical prints - many of them censored - which were used in the press for propaganda purposes.

Further famous examples of censorship in the show include:

* John Calvin's ''Religious Institutes'' (1535), censored by the Church of Rome and condemned by Catholic universities throughout Europe.

* Galileo Galilei's ''Dialogue of the Two World Systems'' (1632). Galileo was arrested for this book, which supports the theory of a heliocentric universe, and the book itself remained on the Index of Prohibited Books until 1828.

* An engraving by William Hogarth (1765) depicting ''John Wilkes in a Liberty Cap.'' Wilkes attacked King George III in his newspaper, the North Briton, and was sentenced to jail for seditious libel.

* Harriet Beecher Stowe's ''Uncle Tom's Cabin'' (1852), said to have incensed Northern feeling against slavery more than any other book. Suppressed in the US South, it sold over 1 million copies in 120 editions elsewhere in America and England within a year of its publication.

* The Woman Rebel, a newspaper published in 1916 by Margaret Sanger, a leader of the birth-control movement. The paper offered advice on abortion and birth control and was condemned for articles of a ''vile, obscene, filthy, and indecent nature.''

* George Orwell's ''Nineteen Eighty-Four'' (1949), in which the author envisioned a totalitarian and dehumanized society where individual freedom and creativity were eliminated. Banned in Eastern Europe, the book created a major stir in the West.

Ann Alter says Orwell's work is particularly appropriate to the censorship show because it issues a warning about contemporary society. ''Technology really dominates our lives. We don't read books anymore. And we digest information through computers and television,'' she says.

However, the exhibit's curator is not without hope. She explains that in the end censorship always fails. ''Books survived because people resisted. And we'll survive because we resist,'' she predicts.

The New York Public Library exhibit, Dr. Gregorian adds, is ''my way of facing 1984 eyeball to eyeball. We are saying 'We shall overcome.' But we must be eternally vigilant. America's freedoms must not be taken for granted,'' he insists.

''Censorship: 500 Years of Conflict,'' which opened June 1, will remain on display through Oct. 15. Meanwhile, NYPL will sponsor a series of related panel discussions, lectures, films, and mini-exhibits throughout the summer. Later the American Library Association and various civil liberties groups are hoping to put parts of the main exhibition on tour across the United States.m