When Youri Egorov finished playing the Rachmaninoff-Paganini Rhapsody last night in his debut with the National Symphony Orchestra, a large part of the audience rose to its feet in a thunderous outburst of applause. Not one of your standard routine standing ovations; this one had real heart.

And it was thoroughly deserved. Egorov has the kind of playing you want in the famous Rhapsody: technique to burn, a feeling for lyric appeal, and a clear sense of delight because it is such a stunning showpiece. You can believe he will be back again often.

Rafael Fruhbeck de Burgos gave the young pianist ideal accompaniment, switching from an inflexible beat that gets you well into the music to sensitively molded rubatos that bring out its soft heart. The orchestra responded with whip-cracking precision.

The other work on the program was the First Symphony of Mahler in a broad-gauged reading that went with more dispatch than some but also penetrated deep into the shifting moods. Fruhbeck knows how to take his time in building the long quiet passages in such a way that the inevitable outbreaks of loud fury make their proper effect.

The horn choir was often in excellent shape, as was most of the orchestra. The opening of the famous slow movement, however, had a kind of sourness that was not intended in spite of all Mahler's grotesque sounds. There were some strangely out-of-tune, blurred notes before the thing got under way. They are likely to be smoothed out by the repetitions tonight, tomorrow and Friday.