Next week (April 14-20) is National Library Week, and I can think of no better time to reacquaint ourselves and our children with the wonders of the public library.

The whole idea of a library is a wonder, when you think about it, especially when you realize that libraries existed before there were books, before there was print, even before there was paper. But the idea of a public library is even more wondrous because the public library may well be the most democratic of all our institutions. It allows everyone to have access to the knowledge that only the rich would have if libraries were not public.The most "educationally advantaged" children I know are those whose parents regularly and frequently TAKE them (not "send" them) to the library. For those of you who are somewhat unfamiliar with how the library is organized, and who want to begin exploring the library for yourselves or with your children, let me today give you a very quick sketch and some ideas to build upon.

The first distinction children need to know when touring a library is the difference between "fiction" and "non-fiction." Books whose stories and characters are imaginary are called "fiction" and are grouped together, alphabetized according to the author's last name. "Non-fiction" applies to all other books - such as histories, science books and books about hobbies - and it is these books that are grouped according to the numbers in the Dewey Decimal System.

In 1876, a librarian named Melvil Dewey invented a system for organizing all non-fiction books into 10 categories. He devised these categories by imagining the questions a caveman might ask to help him understand the world. Information that can help answer the question "Who am I?" deals with philosophy, and so Dewey grouped all the philosophy books together and labeled them 100 through 199. "Who made me?" is a question of religion, and these books are grouped together in the 200s. "Who is the person in the next cave?" deals with sociology, and this group of books was given the numbers from 300 to 399.

There are 10 groups in all, 10 large subject areas, each of which is then subdivided into more specific classifications. The 500s, for example, cover the pure sciences ("What makes things happen in the world around me?"), and the books about one of those sciences - astronomy - are all grouped in a section labeled 520. Within that section, all books dealing specifically with telescopes are labeled 522.2.

Did you ever wonder how libraries were arranged before Dewey invented his system? I am told that many libraries grouped their collections according to each book's size or color. Can you imagine trying to find the specific information you wanted in a system like that? Arranging books according to their specific subject allows for efficient browsing. Once you get into the right category, and locate the shelves whose books deal with that category, all the books in the immediate area should deal with your topic, too. You may go looking for one book and find that it doesn't have exactly the information you want, but its neighbor is right on target.

Libraries contain more than just books, of course, and you should become familiar with the special areas that contain magazines, reference works and consumer publications. Most libraries store newspapers on microfilm, which can be read on a viewing machine that also photocopies individual pages. How about helping your child make a copy of the New York Times' front page for the day he or she was born? How about for the day you were born, too?- Dr. William F. Russell's books for parents and children include "Classic Myths to Read Aloud." Send your questions and comments about Family Learning to him at P.O. Box 1279, Menlo Park, CA 94026.