Period fiction is no gauge of history

America's TV airwaves were recently filled with several hours of engrossing historical drama about atomic scientist Robert Oppenheimer. Viewers were plied with fascinating details about how the United States developed the atomic bomb, and how Oppenheimer himself was eventually destroyed by the military.

When it was over, Americans had an accurate insight into a vital period of US history. Or so it seemed. But did they really?

Critics note that parts of ''Oppenheimer'' were true to history. Other parts were distorted - sometimes grossly distorted - for the sake of a good story, they charge.

The problems with ''Oppenheimer'' can be, and often are, the problems with historical drama of all kinds, whether it is on TV, in the movies, or in such history-based works as ''Gone With the Wind'' or ''War and Peace.''

The problems can be important. As Christopher Collier, a professor of history and author of historical fiction for youngsters, says:

''Most Americans learn most of their 'history' from novels, films, and television.''

This means - even though a lot of historians don't like to think about it - that Margaret Mitchell's ''Gone With the Wind'' may have more to do with the way Americans think about an area like the Deep South than any history professor at Harvard or Yale.

Sometimes the mistakes in historical works are trivial, sometimes more significant.

* John Jakes, who has sold 30 million copies of his pulpy ''Kent Family Chronicles,'' tripped up when he wrote that an Ohio homesteader in 1803 flushed out a pheasant. Fact: The pheasant wasn't introduced into the US until 1890.

* James A. Michener's book ''Hawaii'' tells the story of missionaries and their impact on the 50th state. Fact: Historians say the work of missionaries in Hawaii is misrepresented in the book.

* Nathaniel Hawthorne wrote of the harshness of early New England religious codes in his famous ''The Scarlet Letter.'' Fact: Historians say Hawthorne failed to portray the religious mood of the period properly.

So there is more to writing a historical novel than just including a few words about Washington, Napoleon, or Daniel Boone. The best modern-day writers of historical fiction research their topics like an ivy don.

Gary Jennings, author of the best-selling ''Aztec,'' wondered what he could call the color orange when writing about Mexico 500 years ago. The word ''orange,'' of course, comes from the fruit; and the fruit wasn't introduced into Mexico until the Spanish conquest. After lengthy research, Jennings finally found the word he needed: ''jacinth,'' a gemstone with an orange color.

More recently, Jane Gilmore Rushing, author of the just-published (and excellent) ''Covenant of Grace,'' talked about a chair which she describes in the book with great detail. The chair was used by Anne Hutchinson, an early New England religious leader. Unable to find any historical record of the chair that Hawthorne had said was important to Hutchinson, Miss Rushing could only do her best to describe how it might have looked. The description, though, is so precise that the reader is almost convinced the author had it right in front of her while writing.

The message for readers is: Don't believe everything you read. These books are, after all, fiction. Select historical novels with care.

Even so, there are authors whom both novelists and historians alike admire for their historical detail, and for capturing the mood and feeling of an era.

''War and Peace,'' Leo Tolstoy's masterpiece, is near the top of just about everyone's list. His portrait of upper-class Russian society in the early 1800s combines valuable social and historic insights with a stirring tale.

For two generations, readers have been moved by the saga of Horatio Hornblower in a string of books turned out by C. S. Forester. Not only is Forester's history of the Napoleonic era right on target, but his descriptions of mammoth British men-of-war and how they worked is admired by expert seamen.

Today's novels run the gamut. Some are inaccurate, poorly written costume pieces, in which cardboard characters mouth their predictable lines. Others are well-researched, entertaining, and sometimes beautifully written works.

Despite occasional inaccuracies and sometimes poor writing, historical novels remain among the most popular groups of books. New titles pour from the nation's presses at a phenomenal rate - satisfying millions of readers, and keeping a host of publishers in business.