A treasury of children's books in two volumes; The World Treasury of Children's Literature, by Clifton Fadiman. Boston: Little, Brown. 629 pp. $40.00.

Clifton Fadiman has long been fascinated by words. He readily admits that as a child he grew ''bug-eyed over the miracle of language.'' The past year has brought the reissue of his ''Wally the Wordworm'' (Stemmer House). The ''World Treasury'' brings together the children's books he has enjoyed reading and rereading.

The first two volumes are intended for children 4 to 8; future volumes are to be of interest to children aged 9 to 14. The blue-bound books offer some verses and poems, stories from traditional literature, and texts and selected illustrations of picture books.

The folk tales included, as well as the nursery rhymes and myths, are by and large from European countries. The Aesop of Joseph Jacobs is used, as are his retellings of English folk tales. Spice is added by the modern (and offbeat) fables of Arnold Lobel and Sergei Mikhalkov.

Seven tales of Grimm are reprinted, ''The Shepherd Boy'' being the least well known. These pages, like so many others, carry in black and white the undistinguished decorations and intrusive illustrations of Leslie Morrill. The artist's work is presented in color on the box that packages the two volumes.

Humorous rhymes and poems are scattered throughout the set. Fadiman would have those who might not like verse ''come upon it kind of accidentally.'' From the 19th century there are pieces by Stevenson, Lear, and Clement Moore. Represented by one poem each are Aldis, Coatsworth, Laura E. Richards, and Farjeon. Among the poets who have written more recently for children, David McCord is recognized with four favorites, a group that is prefaced by some commentary about the poet and thoughts that underscore Fadiman's love of words. It is fitting to find in the anthology the delectable ''Alligator Pie'' of Canadian Dennis Lee, and two nonsense rhymes of N. M. Bodecker.

A generous portion of the set is given over to an attempt to share the exceedingly fine picture books of this century, most of which remain in print today. In this regard the anthology is most disappointing. If one is interested in analyzing a text or recalling it, the words are here. However, the picture books chosen reign supreme because texts and illustrations are fully integrated; the interplay is crucial to the telling of the story. An incredible amount of thought had to go into the planning of the initial publication of these works as designers and artists attended to such details as size of page, choice of typeface, and the placement and progression of the pictorial matter. All is lost in the presentation here.

The rendition of ''Make Way for Ducklings'' (a book so carefully executed by Robert McCloskey and his designer, Abe Lerner, that Lerner even chose a typeface that suggested the flip of the tail of a duck) is emaciated, drained of the suspense and joy that have enthralled old and young alike for more than 40 years.

It can only be hoped that Maurice Sendak is spared the sight of this compilation. His ''Where the Wild Things Are,'' which he painstakingly conceived and in which he even makes effective use of double-page spreads without text, is simply not given its due. True, the entire and purposely sparse text is printed, accompanied by a few illustrations that are reduced to 4-inch patches on these pages.

And, to add torment to travesty, the wild things are followed by the calendar book from the ''Nutshell Library.'' No longer a miniature, or a part of a quartet, the verses are plastered on half a dozen pages, five illustrations inserted. This is no way to introduce or recall the boxed set par excellence.

What, then, might be the purpose or use of this treasury? It does let us know what Fadiman has enjoyed during a lifetime acquaintance with children's books. For this the reader can be grateful, for Fadiman brings to the endeavor a greater understanding and appreciation than those of late who have been called upon to evaluate children's literature but bring to their criticism little more than their own childhood or a few beloved titles. Also, his choices are not burdened by being esoteric.

Works that have come from the oral tradition and poems are appropriately read aloud to children, particularly youngsters who cannot yet easily read them on their own. For this the anthology would be helpful, especially if the illustrations were not allowed to impinge upon each child's imagination.

As for the ''classics,'' ''Peter Rabbit,'' and ''The Little House,'' and even the recent innovations of Mitsumasa Anno, children should not be deprived of the pleasure of getting to know these works in picture-book format.