This week's four concerts by the National Symphony contain more surprises than a mere glance at the bill of fare would suggest. And based on last night's which was the first, one can safely conclude that they will not be special just for their novelty, but even more for their substance.

The most newsworthy was the debut for NSO audiences of pianist Peter Serkin. It is unexpected that one of the most noted of the younger victuosos has just now made it to Washington in the concerto repertory-particularly since his celebrated father is such a frequent guest with the orchesta.

Serkin's vehicle was one of the most elegant and lyric concertos since Mozart, the Ravel G major. The composer declared in 1931 shortly after its completion that it was "written in the same spirit as Mozart and Saint-Saens," and that was very much the spirit in which it was played by Serkin, a justly noted Mozart player.

Serkin yielded some of the delicate astringency that some performers sometimes bring to it in exchange for a warmer sound. That is not to suggest that he made any technical compromises; he simply used more pedaling and brought less glittering sound to the frequent high notes than is often the case.

Also new to the National Symphony was the Rachmaninoff 2nd Symphony, with about 10 minutes restored that had been cut earlier by the composer. The performance, under conductor Christian Badea, got more stirring as it went along. The restorations give the famed work an extra bit of harmonic ambivalence.

Totally new to the NSO was Varese's brash "Integrals," an early example of the composer's experiments with "spatial music." Hard to believe, but it was both shorter than the Rachmaninoff restorations and six years older than the Ravel.