Of all the genres in literature for children, poetry may be the best loved but the most difficult to define precisely.

While it is assumed that poetry involves a compactness of text while capturing the essence of a thought, emotional intensity and a rhythm different from prose, the kinds and levels of poetry for children are diverse and often described by how they make the reader feel rather than by a clear-cut definition.For the youngest child, that may mean a blending of nonsense sounds or enjoying a rhyme in a singsong fashion. Young children delight in poems about "self" in a lyrical voice and those that encourage a response with chants or acting out.

For the older child, poetry brings the beauty of language through metaphor, simile and personification as well as the various forms that poetry can take: couplet, tercet, quatrain, haiku and limerick.

Young readers at the junior high level enjoy both narrative and lyrical poetry as they try to accommodate their worlds in objective and subjective ways. This means that sometimes they identify with the poet, while at other times they address the poetry as a personal message. This is why imagery is important in ballads and song lyrics, both of which are forms of poetry for adolescents.

Whatever the piece or the way it is brought together with a reader, Robert Frost suggested that poetry begins in delight and ends in wisdom.

This has been an outstanding year for new poetry books for children and young adults, including collections by individual poets, anthologies of many poets and single poems in lush picture editions.

Among the poets with new collections is Arnold Adoff, recipient of the 1988 National Council of Teachers of English Award for Excellence in Poetry for Children. His book "Greens" (Lothrop, $11.95) is a compilation of poems about the color green and its significance in a child's world. The verses are stylized in typical Adoff fashion, uneven words and lines that make rhythm and syncopation for the reader.

Betsy Lewin's simple drawings add a humorous touch.

A past winner of the prestigious NOTE Award is poet Myra Cohn Livingston, who has collaborated with artist Leonard Everett Fisher in a spellbinding collection of poems called "Space Songs" (Holiday House, $14.95). While the free-verse poems elicit images of the outer world, it is the magnificent paintings that carry this book to its peak. This is a wonderful collection for a starry night, an exploration of space or just enjoyment of two great artists.

T.S. Eliot wrote that poetry is " . . . music heard so deeply/That it is not heard at all, but you are the music . . . ." Some poetry appeals not only for the music but also for the way that sound engages the imagination. One poem collection that utilizes both music and imagination is "Joyful Noise: Poems for Two Voices," by Paul Fleischman (Harper and Row, $11.95). This volume requires a duet-type reading that results in enjoyment of the rhythm and cadence of insect sounds. Printed in side-by-side columns, these poems are read with precision of the click, creep and clatter of a tiny insect world. "Joyful Noise" is the companion volume to "Phoenix: Poems for Two Voices." Both should be enjoyed over and over by willing readers and listeners.

The exuberant, playful and witty poetry of Charles Norman is a triumph to the animal world in "The Hornbean Tree and Other Poems" (Henry Holt and Co., $12.95). Nineteen original poems accompanied by Ted Rand's vibrant full-color watercolors show nature at its most beautiful. From "A Parliament of Swallows": " . . . A thousand swallows perched on wires/ rose as though there'd been a shout,/ And so became a thousand specks/ like pepper sprinkled in the sky . . . " to "A Pride of Chipmunks": "A sire and his cub who dreamed . . . a pride in miniature they seemed . . . , " this collection is most versatile in the number and kind of animals represented in one volume of poems.

Poetry anthologies do not stay in print for many years because of the phenomenal rates on permission-to-reprint. This means fewer anthologies that go out of print sooner and smaller collections that specialize in a topic or theme.

Three large anthologies printed this year will update some of the classical books that have gone out of print. "Rhythm Road: Poems to Move To," selected by Lillian Morrison (Lothrop, $11.95), is a dynamic collection that suggests motion in activities like travel, work, dance and the human mind. "Boogie Chant and Dance," "Times-Square-Shoeshine-Composition" and a hundred more all fit together in one of the most interesting compilations for a long time. No artwork. It's not needed.

A reissue of a volume first published in 1948, "A Rocket in My Pocket" by Carl Withers (Henry Holt and Co., $14.95), is a collection of more than 400 verses that would be considered folklore, created by children and passed on generation after generation. Here are the chants, taunts, brags and tongue twisters of many cultures; for example, "Tat for tat/ Butter for fat;/ If you kick my dog/ I'll kick your cat."

While these are a delight to read (and would have been lost to more scholarly folklore journals), the individual credits are not listed, making it a piece for enjoyment but not one for research in the truest sense of folklore collections.

The most "classical" anthology this year is the reprinting of Walter de la Mare's "Rhymes and Verses" (Henry Holt and Co., $15.95). First published in 1947, this comprehensive volume is and will always be a "period piece" with a tribute to the "rarest and best" verses from an outstanding poet.

Among the several new Mother Goose books published, two need mentioning because of the illustrations that accompany the traditional and first-published verses. "The Glorious Mother Goose" by Cooper Edens (Atheneum, $15.95) is a culmination of rhymes with art by some of the best illustrators from the past: L. Leslie Brooke, Randolph Caldecott, Walter Crane, Kate Greenaway, John Lawson, Arthur Rackham, Frederick Richardson and many more. Each verse is accompanied by two art pieces - a full-page color painting and a smaller black-and-white print - some dating back to the 1800s. "The Glorious Mother Goose" is not only a poetry book but also a classical art collection. An excellent one!

"Tail Feathers from Mother Goose: The Opie Rhyme Book" (Little, Brown, $19.95) is a selection of rhymes from the larger Opie Collection of Children's Literature. The rhymes included are almost all previously unpublished or unusual versions of familiar ones. What is outstanding, besides the verses, is the portfolio of contemporary illustrators, mostly British. Represented are cartoons, expressionist and realistic styles, each one with a personal signature.

Fourteen goodnight poems, two for each night of the week, are found in "A Week of Lullabies" compiled by Helen Plotz with illustrations by Marisabina Russo (Greenwillow, $11.95). Beginning with "A Christmas Lullaby" by Margaret Hillert and ending with Jack Prelutsky's "What happens to the colors when night replaces day . . . ?," the collection includes classical and contemporary poems that can be chanted, sung and memorized as bedtime rituals.

Finger plays and rhymes are another ritual for smaller children, and Sarah Hayes's "Clap Your Hands" (Lothrop, $13) provides the text to some of the most popular action hand games ever known. The age-old "Here Is the Church" and "Incey Wincey Spider" are among the two dozen verses that lend themselves to stretching, twisting and waving hands and fingers. The sweet pastel illustrations by Toni Goffe make this a fun read-aloud book as well.

Two volumes of poems usually considered for adults are also newly edited, illustrated and published in the children's book market. E.E. Cummings' "in just-spring" (Little Brown, $14.95) is a collection of three poems celebrating the images of childhood. Accompanying the verses in the distinctive Cummings style (scattered text in small-case letters) are bold colors and simple shapes that leave the reader to complete the images suggested by the uneven lines of free verse.

"Voyages: Poems by Walt Whitman" (Harcourt Brace Jovanovich, $15.95) is a biographical timeline of the poet's life selected by acclaimed anthologist Lee Bennett Hopkins. Beginning in Whitman's mid-30s and ending in his 70s, the poems are grouped by topics: "Out of the cradle endlessly rocking . . . " and concluding with " . . . So long - And I hope we shall meet again." The stunning black-and-white drawings of Charles Mikolaycak introduce each section and complement the intent of the journey through the poet's life.

Appreciation and love for poetry develop slowly as a result of many exposures and shared experiences. The new poetry from 1988 will offer a rich experience for many young readers.