Jean Pierre Rammpal is flying from Paris. Galina Vishnevskaya arrived by train Monday night from New York; she had flown over from Paris a few days before. Isaac Stern is playing tonight in Philadelphia but will come down immediately after his concert. The English counter-tenor Melvin Earl-Brown, who has been in New York lately, flew down yesterday. And Leonard Bernstein is arriving this afternoon from the secluded spot in New York where he has been composing off and on during his year-long sabbatical from conducting.

Some of the stars of the National Symphony's 50th Anniversary Birthday Gala have already been rehearsing for their appearances tomorrow night in the Kennedy Center Concert Hall. The rest will have their turns this afternoon or tomorrow morning.Rampal will play a Mozart Andante and Rondo and will join Stern and Mstislov Rostropovich in a Haydn Flute Trio. Vishnevskaya will sing Tatianga's Letter Scene from Tchaikovsky's "Evgeny Onegin." Earl-Brown, an Aldeburgh Festival protege of Sir Peter Pears, will add another Russian note when he sings Ratmir's Aria from "Russlan and Ludmila," by Glinka. Stern and Rostropovich will combine their talents in the opening movement of the Brahms Double Concerto, with associate conductor Hugh Wolff directing.

And Bernstein? The word is that he will speak. He will also, for the first time ever, sit down at a Steinway grand piano with Rostropovich, to play Mozart's C Major Sonata for four hands. Rumor also has it that he and his friend Rostropovich will then link arms to play Schubert's convivial "Our Friendship Is Unchanging." (Schubert is very specific about the players linking their arms.)

The program will open with "Slava!", the "political overture" that Bernstein wrote for Rostropovich's first NSO season, and will include the Roman Carnival Overture by Berlioz as well as some unannounced surprises.