There were giants on the Kennedy Center Concert Hall stage last night: Brahms, with his double Concerto, and Itzhak Perlman and Mstislav Rostropovich to play him, with monumental assistance from Max Rudolf and the National Symphony Orchestra.

And when it was over, there were giant shouts of approval from an audience that wanted to repeat its thanks to everyone involved for one of the great performances. What a dialogue Perlman and Rostropovich carried on in the grand work -- their double stopping made their instruments into a matchless string quartet; their volleying of the rapid scales and arpeggios was like having McEnroe and Borg paired up in doubles.

For an ideal account of the Double Concerto you need musicians whose spirits are in tune to each other, and whose essential tone qualties sound like the conversation of identical twins. Last night's performance was ideal. lThe initial attacks were equal in ferocity, the lyrical melodies spun out of both instruments in molten streams. And Rudolf and the orchestra matched the sterling soloists note for note. It is all being repeated through Friday night, and it is all sold out.

After intermission, Rudolf took the orchestra on a loving tour of the great C Major Symphony of Schubert. Like all Schubert, this is music that demands love from its performers. Last night the affection was open and liberal. The orchestra played with inspired tone all evening, the strings' chords at the end of the scherzo were radiant, the brass choir elevated in texture. The oboe solo came out with a lovely lilt.

It is easy to conceive of this music sounding different: The ritard at the end of the first movement was attractive -- less ritard there is better. But Rudolf has known and loved the music a long time, and he and the orchestra played it with all the proper vigor, mixing in a welcome amount of mellowness. The evening began with a solid, if slightly roughened account of the "Magic Flute" Overture of Mozart.