True to its word, the San Francisco Symphony's New and Unusual Music series unveiled something partly new and certainly unusual at Davies Hall Friday night.

Some were appalled by the prospect of it all. Others were amused. All were curious to hear the world premiere of "Plump Jack" by one Gordon Peter Getty struggling composer and also perhaps the richest man in America.

Struggling? Well, given the handicaps of; 1). being the youngest son of a legendary, fabulously wealthy, ruthless tycoon; 2). a reputation as a generous benefactor of the arts; 3). willing to undergo the risk of not being taken seriously as an artist because of the above, Gordon Getty has a lot of strikes against him.

But let's forget about the name Getty and take this 57-minute so-called concert opera at face value, rather than name value. And you know "Plump Jack" is not bad.

The title is a good-natured nickname for the aging, portly knight, Sir John Falstaff. Shrewdly, perhaps, Getty chose to set four Falstaffian scenes from Shakespeare's "Henry IV and V" rather than compete with Verdi's formidable setting of "The Merry Wives of Windsor."

Getty claims that his idioms of choice were Richard Strauss and Verdi, but what actually comes over loud and clear is Benjamin Britten. You can hear it in the extended unaccompanied vocal passages, the understated march in Scene IV, the spare, cryptic, sometimes humorous underpinning by the orchestra.

Yet this music has its own eclectic personality, full of unpredictable quirks and flashes of imaginative color. Getty wouldn't be mistaken for a flaming member of the avant-garde, nor is he a memorable tunesmith, but he holds one's interest with his bag of accessibly tonal tricks. If the gut question of the moment is; would we want to hear more from this composer, the answer would be an unhesitating yes.

There are, however, serious problems with the dramatic structure of this piece. The four sections the first three of which were performed separately on previous occasions do not fuse together; the storyline is episodic, the crucial confrontations diffusely molded. After you get over the shock of realizing that Getty actually has some talent, the first two scenes build a sense of anticipation that the final two could not fulfill.

Getty's "opera" certainly received a sympathetic performance from Andrew Massey and the alert San Francisco Symphony. John Del Carlo made a youngish but authoritatively resonant showing as Sir John Falstaff, and tenor Paul Sperry could expertly point out the words in the parts of Prince Hal and later, King Henry V.

This being a concert performance, the singers had little stage business beyond entrances and exits, and an uneasy spotlight shone upon Sperry when he entered as Henry V. Also the laughing (on cue) San Francisco Symphony Chorus clambered noisily and confusingly onstage in Scene III.

At the close of his work, the grinning, shy, curly-haired Getty took some curtain calls, clapping in a compulsively mechanical manner. The applause, though, was not exactly tumultuous.