With the completion of the fourth and final scene of his concert opera about Falstaff, ""Plump Jack,'' and the premiere of the complete work Friday night in Davies Symphony Hall by the San Francisco Symphony and its chorus and several superb soloists, Gordon P. Getty has good reason to be satisfied, and looked it, as he stood with the performers on the platform, clapping for them with the audience.

He is also faced with a pleasant but difficult question: What now? ""Plump Jack'' in this form is a success on its own terms, and I would guess it is going to be given quite a few performances. The European premiere, by the BBC Philharmonic in London's Royal Festival Hall, is already scheduled for July 19. But as effective as it is in tracing a kind of outline of the story of Shakespeare's fat and rascally but appealing knight, from his pinnacle as the drinking companion and reprobate mentor of Hal, the wild son of King Henry IV, to his rejection and eventual death, ""Plump Jack'' leaves us wishing we had more. These are glimpses -- well-chosen and telling in their effect, but glimpses -- of one of Shakespeare's most memorable and original creations. In about 65 minutes of music, they tell us about him well enough to wish the composer would give us something like the whole picture.

Following the course of ""Plump Jack'' as it has developed over the last two years has also been an interesting study in the character and effectiveness of the score. From the beginning, with Scene 1 as done by the San Francisco Symphony two years ago, it was clear that the orchestra would function in an unusually important way, as a kind of Greek chorus reacting to and commenting on what was being said. With the addition of Scenes 2 and 3, at Santa Clara University last April, Getty's handling of the orchestra seemed more various; individual instrumental voices were speaking out as much as the full orchestra. And the chorus now entered the picture, not only singing but furnishing the hubbub of the crowd at the coronation of Hal as King Henry V.

Scene 1, in the tavern early in ""King Henry IV, Part 1,'' has Hal and Falstaff taking turns pretending to be Hal's angry father. Scene 2, from ''King Henry IV, Part 2,'' shows us Falstaff gulling the fatuous Justice Shallow and then, in a scornful soliloquy, denouncing his lying, boastful ways. Scene 3, longer than the others, is the bitter, humiliating public rejection of Falstaff by the newly crowned King Henry V. Friday night, it was clear that this scene, given excitement and atmosphere by the orchestra no less than by the crowd, and framed beautifully by Gregorian chant authentic to the occasion, is the most powerful and interesting of all.

But Scene 4 turned out to have power of its own. It is the scene from ''Henry V'' in which the death (in bed) of the old knight is described to his longtime confederates by Mistress Quickly, called here Hostess, who ran the Boar's Head tavern and waited in vain for 29 years for Falstaff to marry her. Like the three previous scenes, this one finds its climax in one long speech, and mezzo soprano Clarity James, singing in rich, tender tones, made the moment both beautiful and real by the conviction of her performance. The orchestra, which had reacted to the word ""dead'' in a heartbroken fall of strings, followed her with a commiseration of single instrumental voices. When she said goodbye as Pistol and the others went off to war in France, her ''Farewell! Adieu!'' was clearly addressed to the spirit of Falstaff, and with a whispering snare drum and a long, soft note in the deep strings, the orchestra added its own valedictory.

Now seen whole, ""Plump Jack'' fulfills the promise of its partial performances. What seemed strong before -- especially Scene 3, which is very close to being real theater and not concert theater, what with the crowd and the chant and the ""Hymn to St. George'' and the denunciation of Falstaff by the new king, delivered from the balcony near the orchestra -- seems even stronger.

A fundamental problem also appears. The music the orchestra plays in ''Plump Jack'' is at least as interesting and meaningful as what is sung, but it often constitutes an interruption of the dialogue. This won't do if Getty ever tries to turn the work into a theater piece; in fact, there were times Friday, partly due to some unwise stage direction, when the orchestra's comments, by spacing out the dialogue with unnatural pauses, took away some of the theatrical effect of the scene. Even if ""Plump Jack'' remains a concert opera, it's a problem that should be dealt with.

The performance, conducted by Andrew Massey, was first-rate. Bass-baritone John Del Carlo seemed an ideal Falstaff -- big, rotund of voice, imposing in manner, a real presence in both the flavor and the intellect of the character. Tenor Paul Sperry delivered Hal -- especially the denunciation -- in burningly clear, felt terms. James was an equally ideal Hostess, tenor Michael McCall was a satisfyingly strong Shallow, bass-baritone Arnold Voketaitis sang Pistol with authority, and Peter Lightfoot showed an excellent voice in several smaller roles.