Though Paul Hindemith's Klaviermusik mit Orchester was silenced for more than eight decades by the illustrious Austrian family that paid for its creation, it dangled just out of reach of those who knew of its existence, locked up in a Bucks County farmhouse, with access blocked intractably and repeatedly whenever anyone - whether Hindemith's estate or Philadelphia conductor Jonathan Sternberg - came close.

Finally discovered in 2002, Klaviermusik had an acclaimed 2004 world premiere in Berlin, and will be recorded for the first time, live in concert, at 8 p.m. Sunday at the Kimmel Center with the Curtis Symphony Orchestra.

Not just another Hindemith work, Klaviermusik quickly has become one of the composer's most-played concertos, performed by the New York Philharmonic and San Francisco Symphony, and garnering musical satisfaction that almost justifies the exasperating Viennese intrigue surrounding it.

"It's highly inventive, with a very special third movement," said pianist Leon Fleisher, soloist for the 2004 Berlin premiere and Sunday's concert. "There's an extraordinary duet between the piano and English horn that anticipates Ravel by 10 years." Ravel's Piano Concerto in G has an eerily similar effect.

Yet none of these strokes is particularly arty or oblique. In fact, Christoph Eschenbach, who will conduct Sunday, goes so far as to describe the piece as "very lively . . . not very complicated."

Klaviermusik is from Hindemith's prime years: Though his later music can be dry, contrapuntal and severe, this was written in 1923, when he seemed game for anything: He created scandal with his opera Sancta Susanna's portrayal of a nymphomaniacal nun, then set to work on what was to be his masterpiece, Das Marienleben, a sublime, reverent song cycle about the Virgin Mary.

Klaviermusik was commissioned by Paul Wittgenstein, a fabulously wealthy steel-industry heir who had grown up in family salons hosting Johannes Brahms and other Viennese figures, so that when the promising young pianist lost his arm in World War I, he had the means and artistic pedigree to create a new repertoire of music for left-hand piano. He commissioned nothing but the best: Maurice Ravel, Benjamin Britten, Richard Strauss and Sergei Prokofiev.

Hindemith was among the first and, unlike some of the others, gave Wittgenstein exclusive lifetime rights to Klaviermusik, which he delivered with a playful warning - "You might find it a bit strange to listen to at first" - while also calling the piece "simple," "unproblematic" and something he loved.

It's assumed the pianist didn't share the composer's affection for it. But assumptions don't come easily about this family of eight children, one of whom was philosopher Ludwig Wittgenstein. Three other siblings committed suicide at early ages. When the Nazis were poised to take over Austria, what was left of the Wittgensteins grew hopelessly split: Though the family had been Catholic for generations, the siblings had Jewish forebears, so the sisters cut an expensive deal with the Nazis in exchange for protection. But Paul emigrated to the United States, where he had a midlevel career as a concert artist and taught at Manhattanville College of the Sacred Heart.

The only existing Klaviermusik score was transported - still unplayed - from Vienna to Great Neck, Long Island, where Wittgenstein lived until his 1961 death. Eventually his widow, Hilde, spent her final years in the farmhouse near Doylestown, where all the trappings of the Viennese era were said to have been locked in a single room until her death in 2001, according to Howard Reich of the Chicago Tribune.

Before that, however, any number of people pursued the score. Klaviermusik was always listed among the composer's works, unperformed and "in private hands." Hindemith hadn't kept a copy of his own score. After his 1963 death, neither Yale University, where he had been a faculty member, nor the Europe-based Hindemith Institute could locate it.

Sternberg, now 89 and the artistic director of Bach Festival of Philadelphia, had known of the piece from his years in Vienna in the 1940s. Wanting to give its first performance, he ramped up his search efforts when the score didn't turn up during Hindemith's centennial in 1995.

He never got past the law firms representing the Wittgenstein family. ("I even got friendly with the secretaries. I hoped that would get me to the source of things," he said.) The problem wasn't that Hilde Wittgenstein said no; she didn't reply at all. A 1998 letter from the Hindemith Institute read, "No one except the composer and Wittgenstein know the music of this concerto. No one has seen the score."

The questions are legion. If Wittgenstein didn't like the piece, why didn't he pass it to others? How could a true music lover keep such a major work out of circulation?

One possibility is that he did not in fact dislike it. Hindemith's own description of the piece - straightforward and lovable - seems accurate. Perhaps Wittgenstein always hoped to play it, but never could.

Though he concertized as late as 1960, Wittgenstein's only known recording is a 1937 live performance from Amsterdam of him playing the Ravel Concerto for the Left Hand - and none too well. As if to distract listeners from the parts he couldn't play, he high-handedly added his own flourishes - ones he could play. The Hindemith Klaviermusik is more technically formidable than the Ravel.

"He couldn't do it," Sternberg said. "Those who knew him said it was beyond his capacity."

Performing difficulties, however, had no bearing on why Hilde Wittgenstein refused to even reply to those looking for the score. In the fractious, suicide-prone family, relations were not always cordial, and after the pianist left Europe, according to Reich, he rarely mentioned past ordeals there.

In Doylestown, Hilde went one step further: After her death Sternberg learned that her friends there had little notion of her connection with the illustrious Viennese clan. With law firms guarding her whereabouts, she wasn't simply putting her past behind her, she had made herself virtually unfindable.

In contrast, Klaviermusik itself - the unwilling object of so much secrecy - is like an amiable postcard from a younger milieu, music without shadows. The Nazi takeover of Germany was 10 years away. The polarizing Viennese modernism of Arnold Schoenberg was just a nascent experiment at which Hindemith poked fun: Instead of basing his music on a rigid string of 12 notes, as Schoenberg would, he used the technique with 11 notes. Then there's the English horn solo that ambles through the third movement with few worldly cares.

Had Wittgenstein made the piece part of the past that he buried? Or did he just not want to let it go?