"My dear friends" -- no one else but Mstislav Rostropovich, making his first appearance of the season at Wolf Trap last night, could address in such genial fashion the more than 70,000 people who filled the theater, the lawn and the surrounding hillsides. They had come to hear the National Symphony in its third annual all-Tchaikovsky program and to shower its director with affectionate cheers. Even his surprise solicitation speech after intermission for the orchestra's 50th season -- "Please buy a subscription now and wish a happy birthday" -- received hearty applause.

The thunderous approval given the opening work, Tchaikovsky's Fifth Symphony, was richly deserved. Under inspired and authoritative leadership from Rostropovich, the orchestra gave one of its finest performances to date. Rostropovich can almost always generate enormous energy. Last night proved that, given the right work, he can also channel that energy with single-minded determination to produce a performance of exceptional unity and power. He shaped his orchestral forces with a sure hand, bringing off rich and subtle effects, illuminating the music's every mood. The orchestra's sound had particular depth and an exciting precision. Rostropovich highly insisted that French horn player Edwin Thayer come up front to take a bow for his fluid playing of the famous second movement solo.

This year, Rostropovich added a new twist by making the program a family affair, the first of three such concerts this weekend. Last night was the turn of violinist Pieter Daniel, who is married to the younger Rostropovich daughter, Elena. Appearing as soloist in the Tchaikovsky violin concerto, Daniel showed considerable poise and control as he shared the spotlight with his famous and more flamboyant father-in-law. As usual, the "1812 Overture" with brass in the balcony and cannon booming on the lawn, proved a spectacular close.

The program is repeated Sunday night with the other son-in-law, Alexander Peskanov, in the First Piano Concerto, replacing Daniel. Tonight four family members will be soloists.