London Sinfonietta, Queen Elizabeth Hall, London

The selling point of this concert was the world premiere of Elliott Carter's Dialogues, commissioned by BBC Radio 3 for the pianist Nicolas Hodges and the London Sinfonietta. The programme book had "New Carter" in big letters on its front page, which must have pleased the composer, who flew in specially from New York.

As Carter turned 95 in December, his stamina is a thing of wonder in itself. But for me, the most intriguing piece in the evening was the opening item: Mauricio Kagel's Double Sextet, written three years ago. In this country, Kagel has not achieved quite the fame of peers and contemporaries such as Boulez, Stockhausen or Berio - he's much bigger in Germany, where he has lived most of his life. But Oliver Knussen, who conducted, is a big fan, admiring the precision of Kagel's instrumental imagination.

Double Sextet, for six woodwind (without clarinets) and six string instruments (without viola), has a gritty, throaty sonority, very characteristic of the composer, with many little swooning slides between notes and subtle de- or re-tunings. It begins with a sort of secretive urgency, maintained through much of its 20 minutes, though there's a lovely still section with flutes over string tremolos. Kagel says everything grows organically from the ideas heard at the start, but there is so much incident and variety, it was too much to take in at one hearing.

Like Kagel, Silvina Milstein was born in Argentina, but there all similarity ends. She now lives in this country and teaches at King's College, London. Her Tigres Azules, commissioned and premiered by the Sinfonietta, takes its title from a story by Borges and has something to do with the opposition of known and unknown, routine and chaos, and so forth. Written for a band of 14, the music glitters with a faintly exotic flavour; expectations of continuity are constantly frustrated and the piece seems to become more static as it goes on. And go on it did, though I felt more hesitation than purpose behind its decorative surface.

Augusta Read Thomas is composer-in-residence with the Chicago Symphony Orchestra, which brought her Aurora to the Proms in 2001. In My Sky at Twilight is a setting for soprano and small orchestra of a range of texts, and the composer suggests it's like a fantastic dream. Nothing abstruse there, and to judge by the two works I've heard, Thomas inhabits the broad middle ground of music, aiming to please a wide spectrum. She got enthusiastic applause on this occasion. The orchestral part is euphonious and resonant, often echoing the voice, but although Claire Booth negotiated some of her high arching phrases prettily and her intonation was pure, her diction was so vague I sometimes wondered if she knew what words she was singing.

No such confusion in Nicolas Hodges's spirited dispatch of Carter's Dialogues. It's surely not as economical as Hodges suggested, mischievously perhaps, in his recent interview with The Independent, but it's a great deal more airy and clean-cut than Carter's formidably dense Piano Concerto of 1965. The language is still hard-edged and dissonant (I can't think of another, less loaded word), but many of the gestures are terse, even though the piano part romps athletically over the whole keyboard. My impression was of a pianist provoking and often outwitting the orchestra. The music is like an exchange between personalities, but it seems more a game than a drama. Or perhaps Carter's emotions are different.

'Dialogues' will be broadcast on Radio 3's 'Hear and Now', 10.55pm, Saturday 7 Feb