An odd thing happened at the New York Philharmonic concerts last week. There was insufficient rehearsal time to prepare the scheduled Haydn symphony that was sharing the bill with Mahler's mighty ''Das Lied von der Erde.'' So Zubin Mehta decided to repeat two Webern works from the preceding week's program - the very early ''Im Sommerwind'' and the Op. 6 ''Six Pieces for Orchestra.''
What made this odd, yet altogether welcome, was that Webern, in this centennial year of his birth, is still not a repertory staple in American concert halls. Conductors almost never schedule his works - the longest of which is shorter than the ''William Tell Overture'' - and so audiences have never had a chance to hear his music with sufficient frequency to adjust to the 12-tone idiom, then finally to hear the beauty and the music in those scores. The next step would be a greater appreciation of the important works that these early 12 -tone composers inspired.
Lack of repetition is the biggest problem facing modern music today. Steps are being taken by a brave few to schedule certain major works every other season. These few report that audiences do listen to an unfamiliar work with more care the second time around - even if that second time is a few seasons later.
Anyone can say that audiences resist the stuff with vehemence: Audiences used to resist Brahms, Mahler, and Bartok, but no longer. If the 12-tone works were heard regularly, audiences would adjust quickly and find the best of those works to be quite effective.
another sub 'Das Lied'
Performances of Mahler symphonies are very common these days. Performances of his ''Das Lied von der Erde'' are curiously rare. Mr. Mehta offered a reading of the score last week that never took wing, primarily because the mezzo-soprano - on whom the piece rises and falls interpretively - was wholly miscast.
Brigitte Fassbander has made an important career as a so-called trouser mezzo , i.e., a singer who performs mostly the ''male'' roles in operas such as Orfeo in Gluck's ''Orfeo ed Euridice''; Cherubino in Mozart's ''Le Nozze di Figaro''; Octavian in Strauss's ''Der Rosenkavalier''; and Sesto in Mozart's ''La Clemenza di Tito.'' These roles take a special voice, and it is the very rare singer who can convincingly bridge the gap between trouser roles and other mezzo roles. The one who did who comes instantly to mind is Christa Ludwig: On three recordings she fully communicated the earth-motherish, profound, warmly emotional sentiments.
Miss Fassbander chose to sing with her score in hand. Tenor Jon Fredric West, a last-minute substitute for Jon Vickers, sang his music from memory. Mr. West was totally involved in the drama of his three songs.
Miss Fassbander stood performed coolly, objectively. These qualities are the hallmarks of her career, and she makes them work in the trouser roles. There are other mezzos not so suited to those roles who sing ''Das Lied'' with the needed fervor and warm interpretive insight.
One should not really criticize Miss Fassbander for not making more of the Mahler. After all, someone at the Philharmonic invited her to sing the music with the orchestra. This is the sort of misappropriate artist selection that goes on in too many of the opera houses of America today - casting by name rather than artistic suitability.
Mr. Mehta, who is usually a bastion of sanity in this increasingly insane vocal world, really lapsed here. As a result, his performance of the work faltered, too. Mehta responds directly to the emotional involvement of his soloists. When Mr. West was involved, the conductor transcended himself; but with the aloof, cool Miss Fassbander, Mehta became considerably less inspired.