Delightfully melodious, high-spirited and nonsensical, the movie version of "The Pirates of Penzance," now playing a limited engagement (through March 10) at the Key, can be recommended with only trifling reservations.

Although Gilbert & Sullivan's "Pirates" has scarcely ceased being popular for the last century, its expansive exuberance will reassure both insiders and outsiders that there's still plenty of fun to be had in the company of this particular antique.

Universal's decision to use the film, an unabashed theatrical transposition of the successful New York revival produced by Joseph Papp and directed by Wilford Leach, as a test attraction on so-called pay-per-view cable systems (still unseen in these parts) seems to have caused a rather cavalier approach to the movie's exhibition. "Pirates" wasn't screened for the press, and the distributor, which is renting the Key for this engagement, took almost a week to replace a monaural 35mm print with the advertised Dolby Stereo copy. At any rate, no one in the movie press is getting the impression that Universal looks upon this admittedly specialized light entertainment with enraptured pride and confidence.

Too bad, because it's unlikely that spectators of this generation are destined to see happier, funnier embodiments of at least three major characters--the Pirate King, the Major-General and the Police Sergeant--than the original performances re-created here by Kevin Kline, George Rose and Tony Azito, respectively.

For the past several years an appealing rumor has drifted around that Burt Lancaster would like to make a generation-after sequel to his great comic swashbuckler "The Crimson Pirate," with Lancaster in an elderly reprise of the Capt. Valo role. Surely the emergence of Kevin Kline makes such a project more feasible, since he could take over the strenuous heroic/funny business no longer appropriate for Lancaster. At any rate, a limitless future would appear to beckon to a young actor this handsome and skillful who also displays a genius for playing the fool.

Rose was justifiably irked at the discovery that someone at Universal had nervously clipped a couple of verses from his nevertheless priceless mastery of the Major-General's celebrated entrance number, "I am the very model of a modern major-general." And who can blame him? Rose tosses off Gilbert's avalanching tongue-twisters with such awesome, playful verbal nimbleness that you want to hear him conquer a superfluous challenge like the following cropped stanzas: "I know our mythic history, King Arthur's and Sir Caradoc's,/I answer hard acrostics, I've a pretty taste for paradox,/ I quote in elegiacs all the crimes of Heliogabalus,/In conics I can floor peculiarities parabolous./I can tell undoubted Raphaels from Gerard Dows and Zoffanies,/I know the croaking chorus from the 'Frogs' of Aristophanes,/Then I can hum a fugue of which I've heard the music's din afore,/And whistle all the airs from that infernal nonsense 'Pinafore.' "

Totally new to me, Azito seemed a marvel of long-limbed loose-jointedness, as surprising and enchanting a comic dancer as Ray Bolger at his flexible floppiest. Azito also gives the sergeant a flickering, twinkling facial animation that recalls the early and somewhat lewdly insinuating Chaplin. The movements of Azito and his fellow constables are coordinated with often dazzling herkijerkiness to suggest The Keystone Kops flickering around at accelerated film speed, and the stylization is so effective that it transcends the premise, going beyond affectionate facetiousness into exhilarating comic ballet.

The libretto was intended to ridicule the outrageous cliche's of romantic melodrama, so Leach is always well within his rights in adding fresh comic business to the spoofing prototype. The production is designed with mock-naive sophistication to emphasize the absurdity of it all--a band of pirates notorious for their harmlessness, a juvenile romantic hero mistakenly apprenticed to pirates by a nursemaid who mistook the word "pilot" for "pirate," a male chorus of cowardly bobbies, a female chorus of coyly twittering ingenues, etc., etc.--by juxtaposing inflated romantic sentiments against miniaturized settings.

There's not the slightest attempt to mask the theatrical origins of the show. On the contrary, the settings are deliberately undersized and artificial from the outset. The buildings on the main street of production designer Elliott Scott's Penzance, a town on the Cornwall coast, seem closer to dollhouse than human dimensions, and there have never been phonier-looking cliffs, beaches, meadows and trees than the assortment planted by Scott's crew.

After a rousing start on the toy pirate ship, with Kline striking one hilariously dashing pose after another (I was particularly charmed when he sang a line or two of "I am a pirate king" while hanging upside down in the rigging), the production threatens to get bogged down on the fabricated sands of Penzance Bay while young Frederic and Mabel (Rex Smith and Linda Ronstadt in quite satisfactory re-creations of their original roles) become smitten with each other.

Rose's entrance picks up the slackening pace, and when the scene shifts to the Major-General's country residence in the second act, the movie ascends from one giddy highlight to another. I can't imagine this section of the show being done with more wit or rousing impact. The change is pictorially flattering: cinematographer Douglas Slocombe is allowed a richer, sharper color palette by the shift from daylight on a fake beach to moonlight in pastoral surroundings. Everyone seems to enjoy more room for humorous maneuver in this prettily unreal countryside, and the dance ensembles evoke some of the blithely artificial zest of the segments in the "American in Paris" ballet set against backdrops inspired by the paintings of Dufy and Rousseau.

The best number in the movie carries the blatant artificiality of the backgrounds way up the silliness scale to slapstick genius. It's the Major-General's "sighing of the breeze" song, which finds Rose traipsing and trilling across the bosky Lilliputian landscapes in his nightshirt while the pirates "stealthily" shadow him, seeking cover behind gaily painted moo-cows or, the funniest touch of all, sinking up to their hats while tiptoeing in the middle of a babbling brook.

This is how good "The Pirates of Penzance" is at its most inspired: the trackers submerge, their lost hats seem to float on the surface for a moment and then, as the riverbed evidently ascends, they reemerge with their dripping hats neatly restored to their drenched domes.