American composer/pianist Frederic Rzewski arrived for his concert last night at the Kennedy Center known best as a leading politicizer of the classical music avant-garde.

Rzewski's concern with social issues became well known first from two early works, "Coming Together" and "Attica," both growing out of the New York state prison riot at Attica in 1971. And more recently there were the 36 piano variations based on the Chilean song "The People United Will Never Be Defeated!" that he wrote for Ursula Oppens on a commission from the Washington Performing Arts Society.

Last night's concert at the Terrace Theater consisted entirely of a recent hour-long work for piano and soprano called "Antigone Legend." Its polemics were more implicit than explicit.

"Antigone Legend" sets a version by Brecht of the wrenching tragedy of Antigone confronting the tyranny of Creon. Brecht wrote it as it might have been told in epic narrative two centuries before Sophocles wrote such a play.

The vocal line, projected with skill and nerve by mezzo Kimball Wheeler, mixes complex rhythm speech with expressionistic melodic passages. The singer switches back and forth from the narration to relatively short bits of quotations from the seven or eight characters.

The piano provides most of the theatrical and emotional context (including percussive asides). And the piano part, with its sweeping effects, is the new work's most consistent strength; Rzewski has a fine feel for the piano's sonorities -- and he plays it well.

What might have been an unbroken hour of percussive piano sounds and relatively strident singing fell into persuasive dramatic entities, with genuine sense of mood -- full of mounting excitement in the Theban victory orgy and of horror as the angry elders wring the truth of the army's defeat from Creon.

"Antigone Legend" is an uneven piece, but at its best moments it is powerful. The composer, in post-performance comments, remarked that the piece is still "a work in development." Telling the story of Antigone as a monlogue is confining. The composer's notion that the tale would work better with a visual dimension seems valid.