Steven and his old pal, Phil

In a talk before Tuesday’s Green Umbrella program at Walt Disney Concert Hall, Steven Stucky -- the Los Angeles Philharmonic’s consulting composer for new music, who turned 58 last month -- noted that he had been associated with the orchestra for more than a third of his life and a good half of his composing career. The concert by the orchestra’s new-music group was a 20th anniversary celebration.

The L.A. Philharmonic has been good to Stucky. It, for instance, commissioned his Second Concerto for Orchestra, for which he won a Pulitzer Prize in 2005. This season, he has two Philharmonic commissions: “Radical Light,” which premiered as part of the “Sibelius Unbound” series in October and was taken on tour to Europe last month, and an orchestration of Stravinsky’s “Les Noces” for May.

And Stucky has been good to the Philharmonic. Over two decades, he has played host to composers who cover an enormous stylistic range. He has served as new-music lieutenant to two entirely different sorts of composer-conductor music directors, Andre Previn and Esa-Pekka Salonen. His informal yet informative manner has helped build a large and loyal new-music audience.

Stucky’s openness is a terrific quality in an advocate but a dangerous one for a composer if he wants to remain true to himself. Yet the strange and impressive thing about Stucky’s music is how stylistically consistent it has remained.

Tuesday’s program began with his Piano Quartet, completed in 2005. It ended with “Boston Fancies,” premiered 20 years earlier. Both works follow similar compositional principles and rely on similar musical gestures. The expression in his music has deepened, but Stucky sounds as though he has hardly aged at all.

Still, there are subtle and important differences between his approaches today and 20 years ago. What remains the same are his sunny musical disposition and his love of light. He prefers, when he can, to compose in sunny Italy. And he often notes that when he writes the orchestra the vibrant color of the L.A. Philharmonic is in his head.

In the Piano Quartet, two kinds of light coexist. The piano rings like a bright midday bell. The strings convey a softer luminescence, say the fading sun of a Tuscan summer evening. Stucky described the difference as a clangorous Coplandesque piano (vividly played by Joanne Pearce Martin) meeting Brahmsian strings.

The score proceeds with ease. Lovely sonorities and great sheaves of lyrical lushness invite the ear in. A listener doesn’t have to struggle to follow Stucky’s musical logic, yet one plus one doesn’t equal two.

Happily succumbing to sweet melodiousness and swaying, bouncing-ball rhythms, I just as happily accepted the confluence of Copland and Brahms at the end turning into more mystical piano trills and string textures. Hearing the quartet, I thought I understood everything. Now I realize I can’t reconstruct why it makes sense.

“Boston Fancies,” for a mixed ensemble, is less tricky and more colorful. It functions in a Baroque fashion with recurring stanzas, or ritornellos, and contrasting fanciful sections called fancies. The instrumental writing is full of flavor, as when the flutist (Catherine Ransom Karoly) bent her notes Japanese style while the pianist (Vicki Ray) plucked her strings.

The program showed a more introspective side of Stucky with his short “Dialoghi” for solo cello. It was played with Bachian depth and sweep by Peter Stumpf.

Stucky also invited a favored former pupil, James Matheson, and a colleague, vocalist and composer Susan Botti, to present their work.

The former’s “Songs of Desire, Love and Loss,” which Stucky conducted, illustrates and dramatizes seven poems by Alan Dugan. Matheson tends to build to a punch line, which often helps clarify Dugan’s slight obscurities. You may not know what the poet means, but the music at least directs you to the right place emotionally. Botti, as soloist, supplied heaps of passion.

For the soprano’s own piece, “Jabberwocky,” set to a Lewis Carroll text, she darkened the theater, covered the top of her head and face with a black mask so that only her mouth was visible and then vocally went to town. A percussionist with an elaborate drum set (Roland Vazquez) was the accompaniment. The performance was gripping, but the musical ideas felt thin. Although far wilder and weirder than Stucky, Botti was ultimately more predictable.

mark.swed@latimes.com