CLASSICAL Brahms, Johannes: Symphony No. 1 in C minor, Op. 68. London Philharmonic Orchestra, Klaus Tennstedt, conductor. (Angel digital DS-38091.) - Tennstedt is one of the most exciting conductors around today, capable of inciting orchestras to extraordinary interpretive powers and audiences to near-frenzied receptions. On some occasions, he is unable to sustain that spontaneous level, and in the recording studio, he has been more apt to wax subdued and contained. This performance of the Brahms is a middle-of-the-road, even safe, account of a work that can become emotionally devastating when interpretive risks are taken. But the good news about this disc is that the London Philharmonic, often one of the tamest orchestras in the studio, comes to life for Tennstedt for the first time. Had the maestro asked more of them, the results could have been awesome.