As a rule, conductors do not introduce themselves to new audiences with a piano concerto. However, the Brahms B Flat Concerto gives a conductor more to do than many symphonies.

Thus it was no hardship last night for Neeme Jarvi to make his National Symphony debut in the Brahms masterwork with Andre Watts as his magnificent soloist. Jarvi is conducting the NSO four nights running. On Saturday afternoon he will return to the Kennedy Center Opera House to lead the Metropolitan's "Samson and Delilah."

Watts was in tremendous form. His playing, however, was not a matter of size but of musical imagination that led him to flights of extreme delicacy of touch in fleeing passages and heightened his exciting rhythmic control with accents that may not be indicated in the score but that sound right. In the introduction and again in the slow movement Watts made ritards that were the stuff of dreams. It was on the rock of ritards, however, that he and Jarvi did not always agree. Watts' intentions were entirely clear but Jarvi all too often delayed a split second, thus creating a gap between orchestra and soloist that should not exist.

This is a matter than can easily be adjusted. The orchestra contributed many beauties, not the least of them being John Martin's cello.

Jarvi, as he did in the Opera House, sounds like a practiced routine man who misses too many opportunities to lift performances to the heights. The Berlioz Fantastic Symphony was loud but too much of the time sluggish.