With "Cats" the raging success it is, who can blame the Folger Theatre for taking a chance with Toad, Rat, Mole, Badger, Weasel and a chorus line of multiplying rabbits?

Those assorted creatures, along with a few common bipeds, constitute the general population of "Wind in the Willows," a new musical that received its world premiere at the Folger Saturday night. While many hands have labored industriously on the project, they have not necessarily made light work. This is an evening of unsteady charms and wildly fluctuating merits, the kind of musical that can't be faulted for not trying--merely for trying too hard.

Lightness of tone and grace of means are qualities not often in evidence this time on the Folger stage, neatly disguised as a watery glen. Instead, the musical tends to rely on a hard Broadway sell that is frequently at war with Kenneth Grahame's whimsical tale. Jane Iredale, who has done the adaptation, seems to have experienced severe difficulties getting the story going and keeping it going. To end it, she merely unleashes a free-for-all.

The main conflict is provided by the weasels, a crew of hirsute punk-rockers dressed in studded black leather, who are expanding their territory and moving in on the gentle riverbank animals. Intimidation, bad manners and a sharp hiss are their principal weapons. At the height of their arrogance they storm Toad Hall, ransack Toad's wine cellar and put on grand airs.

Meanwhile, Toad himself has conceived a reckless passion for automobiles, driven into one ditch too many and landed in jail. So there's the matter of engineering his escape and recapturing the occupied castle. And finally romance must be attended to--in this case, between Mole (one of those brains who takes off her glasses, lets down her hair and is suddenly cute as, well, a mole) and Rat, the quintessential pipe-smoking dreamer, who for the longest time can't see that Mole's the mammal for him.

All three of those strands could be woven into a delightful fabric, I suppose, but Iredale's loom is faulty. After a dawdling start--each animal group getting its introductory number--the musical brusquely switches its attentions from one concern to the next and back again. The underlying harmony of this interrelated world--the theme put forth in the concluding "Friendship Song"--is never established. To the contrary, the initial refrain, sung by the rabbits, is one of those typically upbeat opening numbers, in which the rabbits inform us they've been working their tails off getting things ready and will continue to work changing the scenery, playing bit parts, rallying spirits and even counting the receipts in the till. Indicatively, the show that follows often seems to have its nose to the grindstone.

The score, too, is uneven, although there are some sweet contributions (for example, Mole's ballad, "The Day You Came Into My Life"), along with the utterly dispensable pieces (one is a mock calypso, "Large Families," sung by the rabbits again--who else?). In general, composer William Perry has a gift for bouncy, if not exactly memorable, melodies ranging from soft shoe to rock. Roger McGough's lyrics are of a lower order, however, content with banal rhymes, obvious sentiments and some bad punning.

Yet, if you are willing to tolerate "Wind in the Willows" as a hodgepodge with cute ambitions, you may find in it some passing diversions. It has been costumed with great ingenuity by Bary Allen Odom, who has dressed his animals like people, but with an eye for the inventive detail--the swatch of fur or the telling stripe--that actually defines the beast. Likewise, the makeup is subtly revelatory: Toad has big freckles, Badger sports billowing whiskers, and wherever possible, the human nose has been reduced to a button. In that sense, the evening has some of the fun of a costume party--come as your favorite animal.

Set designer Lewis Folden has constructed a magical landscape of gnarled roots, leafy glades, cheerful waterlilies and, although it is really not put to much use, a brambly catwalk encircling the audience. A rowboat glides on among the rushes at one point. Later, Toad's fancy red roadster putters front and center, then explodes into a mass of shiny debris. While the musical itself often seems to be marking time, director John Neville-Andrews and his cast are certainly doing their best to create an impression of activity.

Vicki Lewis, as the love-stricken Mole, and James Mellon, as the oblivious Rat, make an engaging pair of romantics, and never so much as when they are dancing a riverbank pas de deux. John Wylie, as the wise old Badger, sings in 3/4 time about his past triumphs as a boxer, thereby bringing some quiet wistfulness to the proceedings. (There's more than a touch of Gus, the retired matinee idol of "Cats," in him.) P.J. Benjamin overworks the sweaty villainy of the Chief Weasel, and the score has him announcing rather redundantly, "I'm Bad," moments after he's presented similar credentials in "Evil Weasel." Still, he's got energy and a certain slickness of attack.

Only Ken Jennings struck me as actively off-putting, as the hyperkinetic Toad, a role he plays with rather too much self-satisfaction to be truly delightful. Jennings bears certain similarities in size and style to a young Robert Morse, but as yet he has none of the glee that made Morse such a likable devil. On balance, though, it is the performers and the production crew, as opposed to the authors, who give "Wind in the Willows" what moments of enjoyment it can boast.

The authors have taken a classic, distilled it into some relatively formulaic numbers, and replaced its whispering poetry with ersatz pizazz. The million-dollar grosses of "Cats" notwithstanding, anthropomorphism would appear to have its theatrical limitations.

WIND IN THE WILLOWS. Music by William Perry; lyrics, Roger McGough; book, Jane Iredale; directed by John Neville-Andrews; choreography, Claudia Neely; musical director, Donald Sosin; sets, Lewis Folden; lighting, Hugh Lester; costumes, Bary Allen Odom; With P.J. Benjamin, John Wylie, Ken Jennings, Vicki Lewis, James Mellon, David Chernault, Christopher Wells, Anthony Giamo. At the Folger Theatre through Sept. 18.