We have all wondered, from time to time, why a critic as open-minded and musically sensitive as Dr. Samuel Johnson referred to opera as "an exotick and irrational entertainment." A splendid opportunity to answer that question by hearing the kind of opera Johnson was talking about will be available Sunday afternoon at the Kennedy Center. This year's Handel Festival will open with the American premiere of "Poro," a mere 246 years and 11 months after it first took London by storm.

The odds were against "Poro" in February 1731, because Handel did not understand that a German composer writing operas for an English audience might be wise to avoid using a libretto in Italian. But Handel stuck to his guns; through his long career (before discovering the English language and producing "Messiah"), he wrote 40 Italian operas which are now one of the last frontiers of relatively unexplored great classical music. "Poro" was one of the most successful, artistically and financially; it ran for a phenomenal 16 performances in its first season and was revived a few years later. It was helped by some exquisite melodies, a mastery of baroque styles and even more by the participation of two singers: the popular castrato Senesino and soprano Anna Strada whose fans lovingly called her "The Pig" in tribute to her striking appearance.

In Handel's time, opera composers still favored classical Greek and Roman subjects and handel chose a rather obscure one. It seems that during his conquest of India, Alexander the Great ran into particularly stubborn resistance from an Indian king known to Greek historians as Porus. So impressive was a battle that Porus fought on the banks of the river Hydaspes that Alexander, after beating him, restored his kingship (as part of Alexander's empire, naturally) and even enlarged the boundaries of his kingdom. A nice, heart-warning story (they don't make world conquerors like that any more), and one that should make a fair sort of opera - coloful battle scenes, songs like "Stout-Hearted Men," a tenor-baritome duet of reconciliation at the end and perhaps a rousing soldiers' chorus to ring down the curtain.

Unfortunately, no. The style that year was complicated amorous intrigues involving noted figures of history or myth, so the battle is a bit of background in the opera and the spotlight falls on a triangle between Porus (Poro in Italian), Alexander, and Cleofide, a queen from another part of India.

My acquaintance with this opera (almost anyone's acquaintance, I guess, except the people who will be presenting it Sunday) is exclusively through a rather soggy recording made 20 years ago when the opera was revived (in a German translation) for a Handel festival at Halle, the composer's birthplace. The voices are merely (sometime almost) adequate, the conducting sluggish, and the title role is sung by a male non-castrato (you don't get singers with that kind of devotion to their art any more). But through all these barriers, you can hear that some fine music is happening - fine, that is, for those who like banque; don't expect anything like La down'e mobile.

The plot, such as it is, weakens in Act III because the only way all the problems can be solved is by Alexander's deciding to be an extremely nice guy. He was, infact, but it doesn't exactly make for blood-and-thunder drama.

There are moments that struck me as unintentionally funny in replaying the old German recording - notably when Poro confronts Cloofide with an indignant Du Livebst Alexander. It is fummy because 1. He is supposed to be a castrato and you can't help wondering why he cares. 2. Historically, Alexander would probably have been more interested in Poro than in Clexfide, anyway. Sunday, the role of Poro will be sung by Mezzo-socrano Beverly Wolff. I don't know whether that will help.