Antal Dorati is back, and the National Symphony Orchestra and its Kennedy Center audience was glad last night.

The evening, which closed with the Second Symphony of Sibelius, opened with a celebration of the 70th birthday of Samuel Barber, an event that occurred last Sunday. For his notable contributions to every area of music, orchestral song, opera, ballet, chamber music, choral and solo instrumental literature, Barber should indeed be honored by this country. It is reassuring that American orchestras everywhere are marking the signal anniversary.

Dorati began the evening with Medea's Meditation and Dance of Vengeance from the ballet score that Barber wrote for Martha Graham in 1946. Those fortunate enough to have seen Graham dance the work under its final balletic title, Cave of the Heart, will never forget the overpowering effect of Barber's music and the great dancer at her peak. The two famous excerpts from the score, with their emotional balance and gorgeous coloring, have rightly held a high place on American orchestral programs ever since the composer arranged them.

The Piano Concerto, which won Barber his second Pulitzer Prize -- the first was for his great opera, Vanessa -- followed, with James Tocco as soloist. First heard in 1962, the concerto has seemed steadily to increase in stature since that time.

Its exquisite textures, as impressive in the massing of the strings as in the woodwind choir of the finale, are balanced by a keen sense of structure, a factor that is never forced on the listener but that contributes substantially to the feeling of unity that fills the whole.

Tocco proved an artistic powerhouse in the work, not more for the dramatic thrust he provided easily in its largest pages than for the finesse in his gradations of sound, and the fleet beauty of the filigree writing that lifts so many pages to special heights.

Dorati and the orchestra worked in expert tandem alone and with Tocco, to make the conductor's recovery from a minor setback a matter for more than uncommon pleasure.