ONCE BEYOND the Main Reading Room, and the reading rooms for microform and newspapers and periodicals, which anyone over high-school age can use, research purposes become more refined. A number of special reading rooms at the Library of Congress serve more specialized scholarship, ranging from folk music to law.

Some of the more interesting research purposes -- like watching movies in the Motion Picture and Television section, or listening to records in the Recorded Sound Reference Center -- require an appointment. Using these facilities is "not for entertainment," says John Broderick, assistant librarian for research services, "but if you have a good reason to do so." They're limited to research leading toward a publication or a dissertation.

But mere curiosity about your own roots qualifies you to use the Local History and Genealogy section. (Unlike the National Archives, this unfortunately offers mainly secondary sources.) Plan to be inspired here by the wall-size heraldry chart for George Washington, tracing his lineage back to King John of England.

And some special reading rooms are fun just to poke your nose in, like the Hispanic Reading Room, decorated with four rugged murals by Candido Portinari.

The Library understands curiosity. That's why the Mary Pickford Theater plays movies twice weekly for the general public, and 85 different folk recordings selected from the Archive of Folk Culture are available for purchase. And that's why small exhibits in many of the special reading rooms highlight their holdings.

The Music Division, which possesses nearly six million pieces of sheet music and a soundproof room with a piano for playing them, often shows off its original manuscript scores in cases along the hall outside. As consolation for the listening layperson, concerts are held several times a week -- including frequent visits by the Juilliard String Quartet, authorized to play the Library's Stradivari.

In the Rare Book Room, the current show probes the censorship of authors from Ben Franklin to Sam Clemens. Replacing that show in February will be recent acquisitions, featuring "Jazz," written and illustrated by Matisse, and some rare scientific books by Darwin and Harvey.