Paul Henry Lang, the preeminent Handel biographer, calls "Semele" the "first great full-length English opera." And Winton Dean, the extraordinary scholar of Handel operas and oratorios, says that "Semele is the most beautiful opera ever written to English words." That's fairly tall talk, but those who want to know what qualifies the once hotly debated score for such high praise will have a chance to find out a week from today when the Kennedy Center offers the glorious music as the second event of this season's Handel Festival.

When the work was new -- Handel wrote it just over a year after the famous Dublin premiere of "Messiah" -- there was a violent argument in London about whether "Semele" was actually an opera or, like "Messiah," an oratorio. Handel himself was very careful to label it "The Story of Semele, produced after the Manner of an Oratorio."

That ultra-careful designation, however, was purely a matter of the politicking, musical and social, in the latter days of George II, when public morality was thought to be preserved by banning operas during Lent, allowing oratorios in their place. The effect of these bans was sufficiently rigid to cause one of Handel's strongest fans, Mary Delany, to write to a friend, Anne Dewes, the day after the premiere of "Semele":

"'Semele' is charming; the more I hear it the better I like it, and as I am a subscriber, I shall not fail one night. But it being a profane story, D.C. [her husband was the Rev. Patrick Delany and a doctor of divinity] does not think it proper for him to go...."

The "profane" story came to Handel's delighted attention in Congreve's adaptation of the tale as told in Ovid's "Metamorphoses." According to that legend, after Jupiter's love affair with Europa, he again incensed his wife, Juno, by having a new affair in the same family -- with Semele, the niece of Europa and the daughter of Cadmus, the king of Thebes. Semele is on the point of marrying Athamas when Jupiter, through the use of some foreboding omens, interrupts the ceremony and carries Semele off to a private spot he has had prepared for her. Juno, after a lot of private-eye investigations into the goings-on, assumes the shape and voice of Semele's sister, Ino, and in this disguise, with much insinuating, persuades Semele to make a fateful request of Jupiter, which, being granted, can only result in Semele's death.

Here is the basis of an opera plot that has many parallels among operas frequently performed today, the most immediate of these being "Dafne" by Richard Strauss. For Jupiter's regular refusals to behave himself in the manner in which his jealous wife thought he should, he has been a continuing visitor to opera stages since the 17th-century days of Cavalli.

"Semele" is as believable as many of today's most popular operas, whether you look at Wagner's "Tristan" or Debussy's "Pelleas et Melisande." Its action cemters around the kind of oath-taking and swearing that is pivotal in "Salome," with its parallel fatal effect, and the oaths in "Lohengrin," even in "Gotterdammerung."

It is easy to see the matching symbolism between Juno as Ortrud and Semele as Elsa in "Lohengrin," in which, had Elsa only been willing to take Lohengrin on his own terms, she could have enjoyed him indefinitely. In the same way, Semele, had she unquestioningly basked in Jupiter's Olympian love-making, might have lived long and happily in its warmth. But no, she had to ask for the wrong thing, as Elsa did; and for it she, too, died. And it must have been cold comfort indeed for Semele to find out later, in that dubious Elysian field to which she may or may not have gone, that from her ashes a phoenix arose.

Because of the bitterness of the feuding over oratorio and opera in Handel's last days of writing operas, and also stemming directly from his fudging the matter of the proper category for his beautiful new work, Handel saw "Semele" fail after a mere four performances, not to be revived in his lifetime.

Yet there is within the work plenty of solid evidence upon which to agree with Lang's high evaluation of "Semele." As always, the chief question whose answer is the deciding factor in whether a new opera will survive: "What about the music?" For answer, "Semele" is blessed with two of the most familiar and appealing of all Handel arias, the heroine's "Oh sleep, why dost thou leave me?" and, not long after that hit, Jupiter comes out with "Where'er you walk" which has been the delight of tenors and their audiences for over 200 years.

In addition to these are matching gems for the imposing cast of principals which includes Cadmus and Somnus in the bass range, Apollo's tenor at the close, the contraltos of Juno and Ino, and Iris, the soprano who leaps to inform Juno about her husband's dalliance with Semele.

Another of the happiest elements in the opera is that Handel wrote for the same voices that we hear in the roles today: soprano, contralto, tenor, bass, and one counter-tenor. In other words, there is no problem of a castrato and no substitutions are required. The countertenor is Athamas, the bridegroon-to-be whose intended bride is snatched from his sight just as they were about to be married.

The opera also has impressive choral passages. Priests and augurs early in the score are supplanted later by loves, zephyrs, nymphs and swains.

In dramatic variety and in the unbroken richness of its arias, "Semele" is indeed one of the great operas in any language of any era.