Richard Adams' masterful adventure fantasy, "Watership Down," confronts animators with the supreme challenge of transposing a great piece of literature. While it's regrettable that the weakest aspect of the film version, opening today at the K-B Janus and Cerbrus, is the aiimation, much of the original narrative excitement remains intact. Barely adequate as a pictorial rendering of the book, the movie still thrives on the rousing nature of this unlikely but enthralling epic.

Watership Down is a hilly location in the Berkshire countryside. Adams envisioned it as the lapine equivalent of a promised land, the destination of a valiant band of wild rabbits who flee their home warren, whose destruction is foreseen by a prophetic little rabbit named Fiver, trek across 15 or 20 miles of perilous rural terrain and fight to secure a new habitat.

Without violating their animal nature Adams contrived to endow his characters with powers of speech and reason, with a lively culture and myuthology. His own powers of characterization, discription and dramatization tend to disarm readers almost instantly. Adams draws you into his favulous imaginative world so swiftly and smoothly that there's barely time to wave a fond farewell to your skepticism.Within two or three chapters he has achieved an enthusiastic, spell-bound suspension of disbelief.

A British government official who served as a paratrooper during World War II, Adams seems to have bloomed late as a writer, but "Watership Down," which draws on stories he made up for his children and reflects an intimate knowledge of the flora and fauna of the English countryside, provide to be a magnificent flowering. If rabbits actually had a herold literature, "Watership Down" would be their combination of The Odyssey and the Book of Exodus. In his own literary tradition Adams has created a new classic that may surpass "The Jungle Books," "The Wind in the Willows" and the Joel Chandler Harris fables.

It sounds improbable to people who haven't read the book, but Adams generates as much suspense and as many thrills as adventure fans could reasonably crave. No lost desert patrols or intrepid jungle commandos ever faced greater dangers or responded to them more heroically than Adams' skittish but resolute band of outcasts, trying to survive in a landscape that would appear serenely pastoral to most humans.

From the rabbits' point of view, this landscape is alien and constantly dangerous. It conceals deadly enemies and gigantic obstacles, inspiring the runaways to extraordinary feats of ingenuity, courage and endurance. A short distance from their home warren the rabbits must avoid a roving dog by engineering a river crossing that looks impossible for the smallest members of the party, the indispensable, clairvoyant Fiver included. Some quick thinking by the brainy Blackberry pulls them through and creates a precedent for a later, far more crucial river retreat.

Encountering a warren inhabited by oddly melancholy, fatalistic members of their species, the rabbits discover it to be a fools' paradise - plentifully stocked with foodstuffs but also bobby-trapped with snares by the local farmers. After surviving the trek to Watership Down, the rabbits must still establish their new home. A raid on a nearby farm in order to free tame does almost costs the life of Hazel, the group's leader.

Ultimately, the search for mates leads Bigwig, the group's equivalent of Little John or Han Solo, into an undercover mission at a distant warren. The raiders make their getaway with a number of disaffected does but must then stand off a climactic attack by a war party from the rival warren, ruled by a military despot called General Woundwort.

What with one predator or cliff-hanging escape after another, there is rarely a secure moment. If anything, the scenario distilled from the book's episodes by producer Martin Rosen may intensify the melodramatic suspense by jettisoning the breathers and compressing the thrills, which tend to follow hard upon each other.

Individual and social survival always hangs in the balance. It's as if the most exciting attributes of live-action adventure films like "Star Wars" or "Seven Samurai" had been transposed to a strikingly different but still persuasive setting. Hazel and his hardy band really do reproduce the kind of heroic gratification one associates with George Lucas' rebels, Akira Kurosawa's mercenaries or, to recall earlier precedents, Robin Hood and the Merry Men.

The Disney studio might have possessed the resources necessary to do justice to the book. It's unlikely that Disney would have possessed the nerve to depict the violent episodes and climaxes forthrightly. Some of the savagery in the story can't be glossed over; it's too basic to nature and the drama alike.

Martin Rosen, the independent American producer who acquired rights to the book and succeeded in persuading a group of English investors to finance a movie version, seems to have been lucky to salvage a presentable attraction. As admitted novice to animation, he consulted several prominent names in the field, including Richard Williams and Ralph Bakshi, who were committed to other projects, before hiring the late John Hubley to supervise the production at its inception four years ago.

After what he considered a year of dilatory preparation, Rosen dismissed Hubley and assumed directing responsibility himself.

It's apparent that Rosen never found chief animators who could impose a visual scheme as impressive as Adams' literary style. The finished film is clearly dominated by the original author, whose characters and descriptions interjected in the narration spoken by Michael Hordern, seem far more eloquent than the drawings and animated illusions.

This imbalance isn't disastrous, but it is undesirable. Angela Morley's lush, stirring score proves an invaluable collaborative enhancement; it's a heady, expansive musical gloss on the action. Nevertheless, it adds one more aural source of strength to a movie that's already visually undernourished.

Watching "Watership Down," you often feel that the film would be just as effective as a soundtrack album, especially one that incorporated dialogue, thus preserving such wonderfully cast voices as Hordern, John Hurt, Ralph Richardson, Denholm and the late Zero Mostel, who goes out in comic glory impersonating Keehar, an eccentric Levantine seagull who become a one-bird Air Force for the heros after they save his life.

It's not that the animation is a disgrace. There are pleasing touches of characterization and some pretty, misty pastoral landscapes. For example, when the rabbits first glimpse Watership Down, one feels a terrific surge of emotion. However, it depends not on the sight of the Down itself but on Morley's romantic orchestrations and Fiver's declaration. "That's what we should be looking for: a high, lonely place where rabbits can see and hear all round and men hardly ever come."

There is scant illusion of depth in many of the backgrounds. Frequently there's have been drawn. Most of the animals need more bulk, weight and facial definiton. They seem to get flattened against the surface of the screen rather than pulled into an acceptable illusion of three-dimensionality by techniques calculated to emphasize expressions, natural movement and a sense of gravity.

Rosen's production falls far short of the "Watership Down" that might have emerged if all the collaborative ingredients had been equally potent, but the basic material is so good that one never feels bitterly disappointed. Some of the book's wonder rubs off on this seriously flawed yet fascinating adaptation, inspiring secondary collaborators like Morley and Mostel to splendid efforts.

It's a pity that the look of the film never came under the influence of a powerfully motivated and inventive scenci artist. It may have called for a miracle under the circumstances, but Watership Down" is a text that certainly deserved such a miracle.