FEW REPERTORY decisions could have been more unexpected than that of Deutsche Grammophon to record Karl Boehm in the last three Tchaikovsky symphonies. Until about two years ago Boehm's discography was made up almost entirely of Mozart, Haydn, Beethoven, Schubert, Brahms, Wagner, Strauss (R. and J.) and Reger. Since his disc of Saint-Saen's "Carnival of the Animals" and Prokofiev's "Peter and the Wolf" with the Vienna Philharmonic was a bit less than smashing, it is perhaps even more surprising that he would undertake to record Tchaikovsky for the first time (with the London Symphony Orchestra) in his mid-80s.

While Boehm's Fourth (DG 2531.078 and "Pathetique" (2531.212) are eminently sound and unsually musical, I rather felt that a good deal of the enthusiasm expressed over them was generated by the very novelty of his recording such material. Now that the Fifth (2532.005, cassette 3332.005) is to hand, however, the novelty value has diminished and the musical values appear stronger than ever. This is Boehm's first digital recording, and the sound is superb. But its appeal is not that of a sonic showpiece. It is simply a more striking performance than his Fourth or Sixth.

The Fifth has always been regarded as the weakest of Tchaikovsky's great mature symphonies -- the one in which the emotional element seems most likely to overwhelm musical substance. But that substance is really quite considerable, after all, and Boehm seems happy to focus on it and let the emotion take care of itself. It is an approach that has worked well in the past for such conductors as Klemperer, Markevitch, Szell and Krips; Boehm is similarly aristocratic, if noticeably more expansive than any of those four, and he shows as much affection for this score as he does for, say, the big Mozart serenades. It is a refreshing performance, and I would think it would wear exceptionally well.

Otmar Suitner, like Boehm, is an Austrian conductor who began making a name for himself internationally only in his '50s. He is 59 now and, as conductor of the (East) Berlin State Orchestra, he is recording all the Beethoven symphonies digitlly for Denon. The series was launched a few months ago with a first-rate "Eroica" (OX-7202-ND) and continues now with a percentage even more attractive "Pastoral" (OX-7220-ND).

Again, Suitner is generous with repeats; again, his tempi are so well chosen as to suggest there was really no choice at all, and his straightforward phrasing of the well-loved themes conveys more real affection than the gratutious fussing and "molding" so often visited upon them.

While the sonic frame for his "Eroica" was rich and powerful, Denon has issued a disc called "Danceries" (YF-7016-ND), whereon a group so named performs 13th- and 14th-century music from both Europe and Japan on period instruments from both cultures. In the arrangements by Ichiro Okamoto, the group's founder-director, the European and Japanese instruments are heard together, and the resultant sounds and textures are ear-opening in the happiest sense. The 12 pieces may not be equally successful, but the sound of the opening Chanconette tedesche, or estampie from 14th-century Italy, is so piquant and delicious that anyone who hears it is going to have to have this record, whether he gets around to playing the rest of it or not. An enchantment.