The forward momentum so important in a Handel opera was further aided by the treatment of the recitatives. Their function is to define the conflict and motivate the arias, in which the characters express their emotional reactions. Modern performances often suffer from dragged recitatives and unnecessary pauses before or after arias, which put a brake on the progress of the drama. In Handel's day, recitative, defined as a kind of tunable speaking, was declaimed rapidly and flexibly, reflecting the sense of the words. It was never sung with the full voice or in strict time. The object was always to throw the attention forward to the next number, which should follow without a pause. If the opera is properly paced, it will be seen that Handel's unit is not the aria or the scene but the act, even perhaps the entire opera. Every movement contributes something to the integrity of the design; there are very few inert patches, and sometimes none at all.

Handel's manipulation of the convention is also apparent in his treatment of that notorious stumbling block, the da capo aria. The vast majority of his opera arias are in this form, which has two sections, the first repeated after the second and not written out. On the surface, nothing would seem more conducive to monotony. Yet by varying the length and content of the orchestral ritornellos before or after either section, and sometimes omitting one or other of them altogether, Handel can modify the shape of the aria, convey a sense of psychological development, and even deceive the ear into thinking that it is not a da capo aria at all. In a narrowly defined form - this applies to the opera as a whole as well as the aria - even a minor deviation from the norm can produce a disproportionate effect. Again and again Handel leads the listener to expect the conventional thing and then surprises and delights by doing something different. This principle lies behind his whole approach to opera seria. The singer, too, was expected to vary the repeat with improvised decorations; this can be delightful if done with taste, but is often subject to abuse by singers and conductors who have failed to study the correct style, including examples of da capo decoration left by Handel himself.

There should be no danger of monotony in a Handel opera even for a listener who finds difficulty in adjusting to the overall scale. Handel's ear for texture, both vocal and orchestral, and his unfailing melodic and rhythmic resource, afford constant delight. The high voices are not cloying even in an opera like ''Amadigi,'' with no voice lower than an alto. Nor is it true that the operas are inordinately long, provided they are paced properly. The listener who knows Handel only from the New York City Opera ''Julius Caesar'' of 1966 (subsequently recorded) or the Houston Grand Opera ''Rinaldo'' of a few years later, both of which made mincemeat of the design, has little idea how much is missing. To cite a single instance, the transference of Cleopatra's tragic aria ''Piangero la sorte mia'' in Act III of ''Giulio Cesare,'' where she is in chains and thinks her lover dead, to her first meeting with Caesar in Act I, where she is shamelessly putting on an act, makes as much sense as the performance of Lady Macbeth's sleepwalking scene in Act I of Verdi's ''Macbeth'' or Desdemona's willow song in Act I of ''Otello.''

''Giulio Cesare in Egitto,'' to give its full title, was first performed at the King's Theater in the Haymarket on Feb. 20, 1724. It was one of the most successful of Handel's operas during his life and has been by far the most popular in modern revivals. It has the advantage of familiar historical figures, plenty of dramatic incident and a central love story calculated to appeal to the most jaded palate. Cleopatra, setting out to seduce Caesar in order to gain his political support against her brother Ptolemy, finds herself trapped by love. Caesar's dalliance nearly leads to his death at the hands of a conspiracy organized by Ptolemy's uncouth general Achilles. The lovers are united when Pompey's young son, Sextus, avenges his father's treacherous murder by killing Ptolemy.

This is the young Cleopatra of Shaw's play, not Shakespeare's, but Handel endows her with the infinite variety of Shakespeare's heroine. She is one of the most beautifully drawn characters in opera; every one of her eight arias, two duets and two accompanied recitatives contributes to the portrait. She is deepened by experience, beginning as a flirtatious tease, falling in love, and passing through tragedy and despair to radiant fulfilment. Caesar is seen as a conqueror, a just leader, a man overcome by the fragility of human life before Pompey's tomb, a wary politician, a bemused lover, an incensed warrior, a soldier deserted by his legions, before resuming his heroic status. The other characters - the crafty self-indulgent Ptolemy, Pompey's noble widow, Cornelia, the boy Sextus who assumes man's estate to avenge his father, the lecherous double-faced Achilles - are drawn with equal depth and subtlety.

The music, quite apart from its marvelous richness of invention - there is scarcely a weak spot in the score - has more formal variety than many operas of its day. There are three duets (one forming the central section of the finale) and several highly dramatic accompanied recitatives. Caesar's meditation before Ptolemy's tomb is justly famous. No less striking is his monologue early in Act III, a most original compound of aria and accompanied recitative, after he has escaped his enemies by swimming across Alexandria harbor. One of the opera's master strokes is the chord of F major with which this monologue begins following immediately on the E major of Cleopatra's lament for his reported death. Two brief sections marked ''chorus,'' at the end of the overture and in the final ritornello of one of Caesar's Act II arias, where the voices represent offstage conspirators, are not true choruses (they were sung by the available soloists), but they make a strong dramatic point.