Nature: a hands-on approach; The Amateur Naturalist, by Gerald Durrell with Lee Durrell. New York: Alfred A. Knopf. 320 pp. $22.50. Ages 12 and up.

An avid small-animal collector and reader as a boy, I read (and reread) ''Birds, Beasts & Relatives,'' ''The Bafut Beagles,'' ''The Overloaded Ark,'' and all the rest of Gerald Durrell's amusing and wonderful stories of exotic animals in faraway places. But I had so many questions: What animals could I collect where I lived; how, exactly, was I to catch them; and, of course, how should I care for them?

Trial and error sufficed for me. It always will in large part be the method of choice for young naturalists: Things learned the hard way stay learned. Still , Durrell's ''The Amateur Naturalist,'' with its numerous and well-captioned illustrations and its lively text, will reduce the errors and increase the pleasures of the young animal lover. It provides astonishing amounts of information which goes down as easily as if sugarcoated.

After an introduction in which Durrell tells us how he became a naturalist, there are 17 chapters addressing specific habitats (Grasslands, Tropical Forest, Tundra, Cliffs and Dunes, Coniferous Woodlands, and so on) showing and telling about the various plants and animals likely to be found in each.

Want to know about animal-eating fungi, or the courting habits of the waxwing? Interested in building blinds from which to watch animals, or in learning how to make a plant profile? Ever wonder who lives at the bottom of a pond or on top of a mountain? These are the sorts of questions ''The Amateur Naturalist'' answers page after page.

After the impressive lode of nature lore that is the main body of the text, there are several appendixes which deal quite specifically with collecting techniques and equipment and keeping and studying live plants and animals. There is a glossary of difficult terms. The book concludes with a brief essay by Durrell on the future (and important) role of the naturalist.

What makes ''The Amateur Naturalist'' such a fine book has only partly to do with all the useful information it contains. Durrell has always had a seemingly unlimited capacity for the appreciation of any plant or animal. He treats the common and the arcane with equal enthusiasm. Durrell's sense of wonder, his delight in telling stories, his love of nature are contagious. I wish I'd had ''The Amateur Naturalist'' when I was 12.