Saturday night, the Kennedy Center Concert Hall will be infested with frogs, pelted with hailstones and running with blood.

Musically speaking, that is. The frogs will be represented by leaping figures in the strings of the Handel festival orchestra and the voice of mezzo-soprano Rose Taylor. Otherwise, the seven plagues inflicted on Egypt by Moses (including lice, flies and locusts, the death of the firstborn in every Egyptian family, and "a thick darkness . . . even darkness which might be felt") will be the work of the virtuoso Westminster Choir, which will also split into a double chorus to describe the dividing of the Red Sea and the march of the Israelites to freedom.

By the time the chorus tells us "Egypt was glad when they departed," the reasons for that gladness have been made perfectly clear in the most spectacular series of choral descriptions ever composed.

The extravaganza is "Israel in Egypt," by Georg Friedrich Handel, the Cecil B. de Mille of the baroque oratorio. He wrote "Israel in Egypt" in 1739, two years before the "Messiah," and 31 years after his first oratorio, which was done in Italian for performance in Rome.

By that time, he had made two disastrous attempts to found an Italian opera company in London. Seven years earlier he had given his first oratorio with an English text, "Esther," with which he began to take the measure of the English public. When Dr. Samuel Johnson, in his "Dictionary," defined opera as "an exotick and irrational entertainment," he was probably thinking of the situation in the 1720s and '30s, when a German composer was writing operas to Italian texts for English audiences. dandel abandoned Italian opera (for which he had a tremendous flair) slowly and reluctantly, driven out finally by financial insecurity, the fickleness of the audiences, the temperamental storms that swirled around star performers, and above all, perhaps, by the fact that opera had not taken root in England as on the Continent.

While opera was developing elsewhere in the 17th century, England was in the throes of a Puritan revolution which closed the theaters, insisted on simplicity and seriousness in music and forced the nobility (the natural patrons of opera) to maintain a low profile. Even the genius of Purcell, after the Restoration, could not permanently convert the English public to opera, and the situation drastically affected Handel's career in the next century.

His solution, finally, was to get English texts for what remained essentially Italian operatic music, choose "holy" subjects, largely from the Old Testament and the Apocrypha, where most of the heavy action in the Bible is found, and produce a long series of operas, without the expense of scenery and costumers, thinly disguised as oratorios: "Deborah," "Samson," "Belshazzar," "Judas Maccabaeus," "Joshua," "Susanna," ''Solomon" and "Jephtha," to name only the best known.

He was precisely on target with his audience, and the result was that he became the first blockbuster composers -- outside of churchmen like Palestrina -- the first composer whose work has a continuous tradition of public performance from his lifetime until the present.

Bach, who was born in the same year (both will be the subject of lavish attention on the 300th anniversary in 1985) was also one of the first classics, along with Mozart, Beethoven and Rossini, but that did not come until more than a generation after Handel's death. Bach was a cult figure for a relatively small circle of connoisseurs and his major choral works were considered unperformable in public until Mendelssohn conducted the "St. Matthew Passon" in 1829 -- by which time a lot of Bach's music had been lost.

Handel became a classic by outflanking the volatile British nobility, who preferred such long-forgotten Italian operatic composers as Porpora, Veracini, Bonocini and Galuppi. On one flank, his oratorios captured the allegiance of King George III, who generally refused refused to listen to anyone else's music, though he made a grudging exception for Haydn.

On the other flank, he appealed to the rising British middle class, which was attracted by the combination of enjoyment and virtue found in the oratorio form. One mark of a classic is that his work is consciously imitated by other composers, and in this Handel has had a spectacular success. it began with Haydn, whose great oratorios "The Creation" and "The Seasons" resulted from his exposure to Handel during visits to London. And it continued through the oratorios of Mendelssohn, Elgar and Walton, not to mention hordes of long-forgotten Victorians.

Among Handel's oratorios, "Messiah" and "Israel in Egypt" are the most notable departures from Italian operatic style -- "Mesiah" because of its New Testament subject and nondramatic form; "Israel in Egypt" because the real hero is the chorus (though the Kennedy Center performance will include such stellar soloists as soprano Linda Mabbs and tenor Seth McCoy.) Its 39 numbers include 28 for chorus or double chorus, and the long, almost uninterrupted series of choruses describing the plagues of Egypt and the passage through the Red Sea is a major landmark of the choral repertoire.

Besides marking the passage of Israel out of bondage in Egypt (which is why it was chosen for performance during this Passover season), "Israel in Egypt" marks, as clearly as anything in his works, Handel's passage out of bondage to Italian opera.

ISRAEL IN EGYPT -- 8:30 p.m. Saturday at the Kennedy Center.