ARTHUR RANSOME AND CAPTAIN FLINT'S TRUNK. By Christina Hardyment. Jonathan Cape/Merrimack. 224 pp. $12.95; THE WAR OF THE BIRDS AND THE BEASTS AND OTHER RUSSIAN TALES. By Arthur Ransome. Edited and introduced by Hugh Brogan. Illustrated by Faith Jaques. Jonathan Cape/Merrimack. 112 pp.$10.95.

IT IS TIME for Arthur Ransome to capture the American imagination, and if some publisher would only bring out all his books in paperback here, he'd ensnare a whole new generation of armchair adventurers. It doesn't matter that Ransome was a somewhat erratic, globetrotting Englishman with a love of sailing, born 101 years ago in the British city of Leeds; or that he covered the Russian Revolution as a reporter, played chess with Lenin, and married Trotsky's secretary. What matters is that, beginning with Swallows and Amazons, he wrote 12 novels (see box) about children and boats that worm their way into the very fabric of childhood. One Ransome reader will recognize another whether he be 8 or 80.

Only reading the books to children or with children will make true converts, but Christina Hardyment has written the ultimate volume for the fanatic. She has followed Ransome from haunt to haunt, from Cumberland to Norfolk, identified and mapped the actual places that he has incorporated into his stories, talked to those who remember him and tracked down the now aging children who served as models for the crews of the Swallow and the Amazon.

What emerges most strongly from her labors, affectionately and straight forwardly recounted, is the concreteness of everything he wrote about: the handmade Jolly Roger flag still saved by one family, the farmhouses unchanged by the edge of the lake, even the original Amazon dinghy still moored in a boathouse after 55 years: "Five minutes later I was satisfying the ambition of a lifetime: rowing the original Amazon on to the lake and towards the Octopus Lagoon," she writes. The fantasies of a true fan fulfilled.

Hardyment has also delved into Ransome archives both at Leeds University and the Abbot Hall Museum. At Leeds she found his cabin trunk, much resembling the one containing Captain Flint's hidden treasure in S&A, full of notes and photographs. Hugh Brogan has already written Ransome's authorized biography; but Hardyment's purpose is different and singleminded. She wants more. She wants to know where the children bought milk, where they slid down the mountainside, or saw the charcoal burners. Why? Because Ransome's children are her friends. They occupy a special place in her imagination. She is a pilgrim.

Not all her subjects proved to be totally happy with their legacy as models for characters in books familiar to generations of inquisitive British children. Susan Altounyan, the model for Susan Walker, mate of the Swallow, "hated the pall of respectability which the Susan of the books wished upon her." Mate Susan was always worrying about wet feet and nutritious food. Titty Walker's real-life counterpart lives on the shores of Coniston Water in the Lake District. She admits to some difficulty as a young child in distinguishing between her own personality and that attributed to her by Ransome: "I do remember trying to be as Tittyish as possible," and insisting that she was not nearly so literary or imaginative as the Titty in the stories. Ransome himself made the distinction "They were real children," he said, "but now they've become something quite different; they're from my head."

But for those who've asked questions, who've identified with Ransome's children, the answers are here, or at least as many of them as we shall probably ever get. One is glad to have someone follow this trail before it grld and especially glad to see the wonderful black-and-white photos of the original children, who all look so satisfyingly as they should. Captain Flint's Trunk is a book to be read only after the Swallows, Amazons, Death and Glories, the Hullabaloos and the Mastodon have dug themselves thoroughly into the mind.

ARTHUR RANSOME'S first best- selling book was a series of retold Russian folktales entitled Old Peter's Russian Tales (reissued last year). It was the enterprise that took him first to Russia in 1913 and inspired his study of the Russian language. After their great popular success, Ransome attempted to write a companion volume but ill-health and the Second World War prevented him. Some further tales were retold and some of them are collected in The War of the Birds and the Beasts by his biographer Hugh Brogan.

Ransome is a spinner of yarns and the rhythms of these old tales remind one of the campfire, faces in the flickering light. The swan princess longs to fly south and leave her earthling prince and baby son; the sparrow and the mouse quarrel and end up involving all of the forest in their battle; the soldier defeats death and ends up seeking entrance to the afterlife. The story moves on. The sentences flow: "And the earth opened." "And the flock of wild swans flew down towards the house." "And the drover calls for a glass of vodka." Great stories for reading aloud even without a campfire.

Brogan fills us in on the first stirrings of the master storyteller, a tale in itself: "Arthur Ransome became a writer at the age of eight, or so he said. He was playing a game of ships and the sea (of course!) with his sisters and brother one day, during which he hit his head very hard on the underside of the dining-table. This accident is supposed to have set free his powers. In the afternoon he wrote his first tale, about a shipwrecked sailor on a desert island." Happily for us all there were more islands, more shipwrecks and many, many more tales.