What is at stake here is not merely whether a single note in a huge symphony is being played too loudly. The larger issues have to do with overall atmosphere and performance tradition. By distorting the dynamic of the final note, conductors shatter the fragile musical atmosphere Mahler so carefully created to end the movement and to prepare the listener for the shock of the opening of the second movement, marked ''Stormy, with the greatest vehemence.'' Conductors who vehemently attack the last note of the first movement jump the gun on the atmosphere Mahler wanted to save for the second.

So how to explain decades of performances and recordings with ''savagely final punctuation''? Perhaps it is simply a matter of conductors' blindly following a false tradition. If so, it started at least as early as 1947, when Bruno Walter made the first recording of the Fifth. Great weight is often attached to Walter's performances of Mahler, for as a Mahler protégé he was present when the composer conducted some of his own symphonies. Yet other conductors, including Otto Klemperer and Willem Mengelberg, were also close to Mahler and heard him perform, and many of their interpretations are quite different from Walter's. One should also bear in mind that Walter recorded the Fifth more than 35 years after Mahler's death.

Some conductors remain unconvinced that Mahler wanted the note played softly. If he did, they ask, why didn't he put a separate dynamic on the note itself? Isn't the sf standing alone, 13 measures after the pp marking, a bit ambiguous? Couldn't it be that Mahler, like some later composers, used sf independently to mean loud? Isn't it plausible that he wanted the movement to end not in soft resignation but in loud protest? Is there any evidence from Mahler's own performances?

These are reasonable questions. Mahler was not always consistent in his markings. Yet a substantial chain of evidence, reported here for the first time, leaves no doubt that Mahler wanted the note played softly.

For one thing, he marked the note to be played softly from the beginning. In his original handwritten score, he wrote pp on the note itself, and pp also appeared in the first published edition.

After conducting the premiere in Cologne in 1904 and a second performance in Hamburg in 1905, Mahler changed the pp to p, a modest boost in dynamics. He also added an accent.