On Sunday afternoon, Van Cliburn sat down at his Steinway on the stage of Symphony Hall and launched into a richly harmonized and floridly decorated arrangement of “The Star-

Spangled Banner.” Unaccustomed to such a recital prelude, listeners exchanged bemused glances and hesitantly rose to their feet.

Their puzzlement would not have been possible 40 years ago, when Cliburn was triumphantly touring the country as a national hero. The tall, gangly Texan, with his trademark shock of wiry blond hair, was a cultural and political icon. In the unlikely arena of classical music, he had come to represent America the invincible, America the free. At a time when American pride was smarting from the Soviet Union’s success in launching a space satellite before we did, the 23-year old Cliburn had beaten the Russkies at their own artistic game. Virtually unknown (although he won the Levintritt Foundation Award in 1954), trained almost entirely by his mother (although he entered Juilliard at 17 to study with Rosina Lehevinne), the young pianist had won the first Tchaikovsky International Piano Competition in Moscow in 1958. It is said that he conquered the hearts of the Russian people (there were listeners in the audience Sunday afternoon who had heard his Moscow performances and remembered how thrilled they were to see the victorious young American). And when he returned to the US, Cliburn was celebrated in a ticker-tape parade in New York City and went on to a spectacular concert career. Under the circumstances, it would have been surprising if he hadn’t opened his concerts with the national anthem.

After more than a decade of intensive concertizing, though, the Cliburn phenomenon seemed to burn out. Perhaps it was his own exhaustion. Perhaps it was the critics’ increasingly negative reviews. Perhaps it was the country’s swing to the left, its repudiation of America’s role in the Vietnam conflict. Whatever the reason, about the time that it became unfashionable to be openly patriotic, Cliburn gradually cut back and retreated to his home in Fort Worth. His last recital appearance in Boston was in 1971.

Although he performed rarely, Cliburn continued his musical pursuits. He continued to play privately and he cultivated the Van Cliburn International Competition, which he had founded in 1962. Then, in recent years, he began to emerge, however slowly, from his long “sabbatical.” There was a White House performance honoring Mikhail Gorbachev in 1987, a number of gala concerto performances, a return to Moscow in 1989, the re-release of some early recordings, and recitals in carefully selected venues and on special occasions. Then, in 1999, after appearances with the Boston Symphony Orchestra at Tanglewood, he expressed a desire to play a recital at Symphony Hall. The FleetBoston Celebrity Series was happy to arrange it.

So, when he appeared Sunday afternoon, dressed impeccably in an afternoon suit and as tall and slim as ever, it was before a full house of listeners curious to hear what he sounded like after all these years.

In choosing his program, Cliburn spared himself nothing. Among the things he may have wanted to prove was that he still has bravura technique comparable to the best of the international virtuosos’. This he did in his extraordinary performance of the Etude for Octaves by Debussy, in the iridescent rippling of notes in “Reflets dans l’eau,” and in dazzling chromatic-scale passages in the Chopin F-minor Ballade.

That he can produce an enormous sound was also clearly demonstrated throughout the group of Brahms pieces, particularly in the Two Rhapsodies, Op. 79. Many in the audience were clearly thrilled by the playing, although I found Cliburn’s sonority relentless in its granitic solidity, its unvaried color and dynamic range, and its scarcity of legato.

In several of the more lyrical Brahms pieces, like the E-flat-minor Intermezzo, Op. 118, No. 6, Cliburn almost routinely ignored the composer’s dynamic markings, seldom playing a true pianissimo or differentiating between a forte and a fortissimo. In the more extroverted pieces, including the rhapsodies, he again skimped on the quieter end of the dynamic spectrum and shifted into overdrive in the louder sections, with the result that everything sounded thick, harsh, and muddy.

Cliburn’s playing of Chopin offered mixed blessings. The familiar A-major Polonaise was, to these ears at least, unlistenable. The sound was inexorably percussive, the phrasing square and clipped. It seemed to go on forever. In the Ballade and the C-sharp-minor Scherzo, there were some brilliant passages — tireless octaves, ascending chords with broken-octave bass — that were truly exciting. But there was no melting lyricism to serve as a counterpoise. The pianist was at his best in the Debussy selections, including a magical evocation of moonshine in “La terrasse des audiences du clair de lune.”

There were four encores of pieces by Rachmaninoff, Chopin, and Schumann. Basking in the crowd’s enthusiasm, Cliburn delivered a graceful little speech paying tribute to Boston audiences and to Symphony Hall on its 100th anniversary. Then he sat down and played what may have been the afternoon’s most perfectly realized work, a transcription of Schumann’s lovely song “Widmung.” The title means “Dedication,” and the performance seemed to sum up Cliburn’s own dedication, however circuitous a path it may have taken, to music and to his listeners.