"Camelot," that most lavish of musicals, comes bedecked with all the pomp and pageantry of King Arthur's England. But its epic ambitions are deceiving. It is really built upon a simple foundation: the romantic triangle formed by Arthur, Guinevere and Lancelot. If we do not feel equally for the three of them, the show lists terribly and all the sumptuous decorations begin to look hollow.

That is precisely what is happening at the Warner Theatre, where "Camelot" has set up its turrets and tents through April 4. And the weakest performance is the very one you would expect to overpower the others--Richard Harris' Arthur. Harris is no Richard Burton, the original Arthur. (Not even Richard Burton is Richard Burton these days.) But that's hardly an excuse for Harris' curiously quixotic portrayal, which alternates between lows of sour indifference and highs of pure histrionic ham.

Since Guinevere is played by Debra Dickinson, an actress of ravishing grace, and Lancelot by a dashing Richard Muenz, you may be forgiven for hoping that the two will hotfoot it off to France as soon as possible. That, of course, would not be in the best interests of the musical, which spends two rather extended acts convincing us that all three characters, torn between their passions and their ideals, are caught in an impossible situation. Still, it does seem like a way out.

"Camelot's" awkward book was never its strong suit. What it had-- and continues to have--is a first-rate score by Frederick Loewe, profligate with the kind of stirring and lilting melodies that seem to have vanished from our musical stage. Alan Jay Lerner's lyrics don't quite match those he wrote for "My Fair Lady," but they're consistently literate and often moving. There may be other ballads as haunting as "If Ever I Would Leave You." But listen to the controlled ardor with which Muenz sings it to a chaste Dickinson and you may not think so. Dickinson returns the lovely compliment with a heartfelt rendition of "I Loved You Once in Silence." Even the title tune has taken on extra resonance, as the unofficial anthem of the Kennedy presidency.

When Harris chooses to abandon his vocal tricks and his calculated appeals to the back row of the balcony, he is not without gifts. He is probably too weathered to be very convincing as the young Arthur, who shies away from the handsome woman soon to be his queen and stumbles over his half-formed notions for a Round Table. But as the older Arthur, who has learned that ideals are weighty baggage to carry through life, Harris has a world-weariness that is on target. The ultimate irony is that he can be charming, whenever he stops trying to ingratiate himself to an audience.

As touring shows go, this one is far more bounteously produced than most and makes the recently departed "Chicago" look like Dubuque in retrospect. There's been no pruning in the chorus ranks, the costumes are appropriately extravagant, and the sets suggest the sort of great, gilded cobwebs spun by the more imaginative magicians of antiquity. Such surroundings certainly help to justify the roaring and flailing of James Valentine, whose Merlyn seems to be patterned after Lear on the heath. Perhaps, one could wish for a more disciplined Pellinore, that silly king made even sillier by Barrie Ingham, and a more devious Mordred than Richard Backus. But neither performance does much harm.

The real blows are delivered by Harris, a knight in tarnished armor, a king of erratic command, a lover too much taken with his own image. Because of him, "the fleeting wisp of glory" that was "Camelot" proves all too fleeting this time.

CAMELOT. Book and lyrics by Alan Jay Lerner. Music by Frederick Loewe. Directed by Frank Dunlop; sets and costumes by Desmond Heeley; lighting, Thomas Skelton; choreography by Buddy Schwab; musical director, Franz Allers. With Richard Harris, James Valentine, Debra Dickinson, Richard Backus, Barrie Ingham, Thor Fields, Richard Muenz. At the Warner Theatre through April 4.