IF ever anything amounted to more than the sum of its parts, it is Tommy Smith's new arrangement of Chick Corea's Children's Songs for himself on tenor sax and the virtuoso strings of the BT Scottish Ensemble, premiered in Perth on Wednesday, reaching Glasgow tonight.

And if ever the word ''arrangement'' was an inadequate description, then this is the occasion. Corea's piano pieces are justly famous as charming miniatures. Smith has played (and recorded) some of them before, with pianist Murray McLachlan. And there is a version arranged by saxophonist John Harle.

But Smith has gone way beyond these in an adaptation that is nothing less than a recomposition. He has completely revisualised the music, using about 17 of the pieces as a basis for a huge, and immensely unified, suite for tenor sax and strings. It runs at over 40 minutes - he played it in two parts, straddling an interval - and, in an unqualified triumph of composition (not mere transcription or arrangement), has produced what must be not only one of his own most important pieces of work, but a major opus for strings and sax.

It transcends technical and stylistic barriers between written and improvised music while resulting in a composition that preserves absolutely the character of the originals. The string writing - superbly played by Clio Gould and her group - is wide-ranging and of a technical level that is light years beyond Smith's first forays into mixed genres. I reiterate: a top-drawer new work. It demands a major festival showcase, and a recording. Grippingly performed, it was the centrepiece of a concert that displayed Clio Gould and her group in bracing form in music by Roussel, Ravel, William Schuman, and - with alto saxman Christian Forshaw and his spellbindingly sophisticated playing - Richard Rodney Bennett.