Henry Purcell's (and John Dryden's) operatic extravaganza "King Arthur, or The British Worthy" dates from the spring of 1691, and the Washington Opera production, imported from the Opera Theatre of St. Louis, is the liveliest 300-year-old piece of musical theater we are likely to see this season.

Do not go to the Kennedy Center's Eisenhower Theater, where it opened Saturday night and will have 10 more performances through Feb. 2, expecting anything like "Camelot," "The Once and Future King" or the great prose epic of Sir Thomas Malory on which most of our Arthurian fantasies are based. What we have here is more like a baroque answer to "Cats." There is no Lancelot, no Guinevere or Mordred, but a series of spectacular production numbers with only the slimmest pretext of plot or theme to string them together; something to entertain the tired businessmen of William and Mary's London and send them home whistling. The characters are one-dimensional, and the technology is not as advanced nor the plot as well elaborated as in "Les Miserables" or "The Phantom of the Opera." But the music is considerably better and some of the singing is spectacularly good.

The story, such as it is, concerns the struggle between Arthur, King of Britain (baritone Kurt Ollmann) and Oswald, King of Saxony (tenor Carl Halvorson) for two prizes: control of a united England and the hand of the beautiful, blind Lady Emmeline (soprano Sylvia McNair, on opening night), daughter of Conon, Duke of Cornwall (baritone Bradley Hayes). Besides Arthur, the only familiar character is Merlin (bass-baritone Kimm Julian), a figure who can overshadow the king and sometimes does in this production, riding about on a dragon that is downright cuddly and producing claps of thunder, billows of smoke, random explosions and magical panoramas that are undoubtedly what made the tickets move in baroque London.

Oswald also has a house sorcerer, Guillamar (baritone Gordon Holleman), and the show uses the struggle between the two magicians as a pretext for its most striking moments. Each sorcerer has a subsidiary sprite to take care of the detail work, and these are two of the show's most juicy roles: Philidel ("an airy spirit," sung by soprano Elisabeth Comeaux) works with Merlin; Grimbald ("an earthy spirit," sung by bass-baritone Kurt Link) handles dirty tricks for Guillamar and supervises a core of demons, some of whom look like punk rockers. Link throws himself into this role with energy, gusto, a flavor reminiscent of the late John Belushi and an impressive voice. He is also assigned to sing the "Cold Genius" (a sort of animated snowbank who personifies deep winter) in the "Frost Scene," the most spectacular of many irrelevant but delightful production numbers. Aided by a skilled chorus and Rebecca Abram in the role of Cupid, he brings out the full potential of this music, which rivals Vivaldi's "Winter" Concerto and Vaughan Williams's "Sinfonia Antarctica" as a musical evocation of cold weather.

The trio of Merlin, Philidel and Grimbald inevitably recalls that of Prospero, Ariel and Caliban in Shakespeare's "The Tempest." The resemblance is probably strong enough to convict Dryden of plagiarism, but that does not make it less enjoyable. Comeaux, as Philidel, will probably make you think of Mary Martin in "Peter Pan" and may recall Beatrice Lillie singing "There Are Fairies in the Bottom of My Garden" for listeners of very wide experience. In the "Bog Scene," where Philidel and a chorus of kindred sprites save Arthur and his army from being lured into a quicksandlike trap set by Grimbald, the effect comes perilously close to something out of Gilbert and Sullivan.

At other times, this show verges on the spirit and style of a school pageant -- but a school filled with adult professional entertainers. Some of this is deliberate -- the grand finale, for example, where Arthur and Emmeline are crowned amid a patriotic panorama that includes the allegorical figure of Britannia (who steps into the scene from a giant British penny), Queens Elizabeth I and Victoria, Kings Henry V and Charles II and, rather incongruously, George Washington carrying his famous hatchet. It's almost enough to make you want to go out and conquer India or colonize Australia all over again.

The budget for this production was obviously not unlimited, so the armies of Arthur and Oswald (which seem to have some interchangeable personnel) are decked out not in medieval armor but bluejeans with uniform tops. Knights in shining denim?

On the other hand, there is considerable skill in the stage direction of Colin Graham, who first devised this edition of "King Arthur" for the English Opera Group in 1970, freely adapting Purcell and Dryden's original and slipping in some music that Purcell wrote for other occasions -- doing to Purcell and his collaborators the kind of thing that they often did to their own works, to Shakespeare and other works of the past. Two scenes reflect obliquely on the other attraction currently playing in the Eisenhower because they show how parts of "The Magic Flute" might have been made more effective. One is a scene where Guillamar tries to force himself upon Emmeline, who has been kidnapped, and it has a touch of terror absent in "Flute's" similar scene between Pamina and Monostatos. There is also a fine scene in an enchanted grove, where Arthur is subjected to a variety of temptations, that evokes a feeling of the supernatural absent from "Flute's" scene of ordeal by fire and water.

The most treasurable part of "King Arthur," of course, and the only thing that has kept Dryden's text alive for 300 years, is Purcell's music. The composer died young (his dates are 1659-95), but he was one of the giants of the baroque era. In a time and place where musical theater was in a state of abysmal decadence, he managed to write a wealth of theatrical music that transcended the limits of its origins, and "King Arthur" is a prime example. Conductor Stephen Lord gives a solid account of it without trying to include fine points of baroque performance practice in this very modern adaptation.

Two of the singers are Washingtonians: tenor Robert Baker, who has sung several small roles commendably with the company before; and Willow Johnson, a mezzo-soprano of great promise making her company debut.

Most of the others, brought in from the St. Louis production, are singing here for the first time and many would be welcome back. Perhaps the most spectacular voice in the production is Abram, a coloratura soprano hidden away in the tiny role of Cupid. McNair is also impressive as Emmeline, not only for tone, control and clarity of diction but for a high level of emotional involvement in her role. Halvorson as Oswald has more appealing music than Ollmann as Arthur and sings it with a fine, clear tone and a good sense of style. Ollmann's voice is good, but he sometimes uses more vibrato than this kind of music should have. Link frequently steals the show, partly because he is given prime material to work with but also because he knows what to do with it. His was a most auspicious debut, and I hope to see him at the Kennedy Center again.