President Reagan proclaimed today Andrei Sakharov International Day, in honor of the 62nd birthday of the Soviet human rights activist. Last night, the elite, the opinionated and freedom-lovers of various nationalities gathered in London, Paris, Marseilles, Tokyo, Amsterdam and the Kennedy Center Terrace Theater in Washington to honor Sakharov, who has lived in internal exile in the Soviet Union since 1980..

At the Kennedy Center, the Soviet Emigre' Orchestra and mezzo-soprano Renata Babak gave a performance billed as a benefit the Sakharov International Committee, but the music often took a back seat to the program's political overtones. The last scheduled selection, Shostakovich's Prelude and Scherzo, Op. 11, provided the precise summation of the spirit of the evening: a framework stuffed, perhaps overflowing, with unbridled ideas of good and evil, beauty and ugliness.

The eight announced (and four unannounced) works were accessible, easy to assimilate and wisely designed for an audience more attuned to a social, rather than musical, evening. Conductor and violinist Lazar Gosman opened with Mozart's whimsically scored Serenade No. 6 ("Serenata notturna"), K.V. 239, with its playful tympani punctuation and double bass substituting for the cello in the solo quartet. There was no mistaking Gosman's dominant role in the orchestra's personality; his violin trod where the angelic ensemble feared to follow.

Two works by Tchaikovsky dominated by Gosman's singing strings, pure tone and faultless technique concluded the first half; the second half divided sets between Babak and the orchestra--and conquered.

Babak, an e'migre' like Gosman, an expressive mezzo and an impressive actress, swooned listeners with works by Kos-Anatolsky, Puccini and, again, Tchaikovsky. Babak's personality is as pleasing as her formidable voice; pianist Frank Conlon and flutist Katherine Burdick were recalled onstage by Babak, a gracious gesture of thanks for their beautifully controlled, understated accompaniment.

Purcell's Chacony marked both the orchestra's return to the center of attention, and the first work that they played in true ensemble form. Finely honed color, churning rhythms, harmonic contrasts and breathtaking musicianship swelled from Gosman's arrangement for chamber orchestra of Shostakovich's powerful work.

For Sakharov, whose sacrifices, exile and physical deterioration overshadowed the night's proceedings, the benefit's organizers let in a little sweetness and light: the final encore, a thunderous rendition of "Happy Birthday."