The Tokyo String Quartet, in its Corcoran Gallery concert last night, gave Alban Berg's early quartet ideal companions in Mozart's late D Major Quartet, K 575, and Mendelssohn's early Opus 12 in E Flat.

The four musicians proved so perfect an ensemble that it was difficult to remember that first violinist Peter Oundjian joined his three companions only last season. They are as well matched as the Amati instruments they play. Not merely in balance, but in intimate details in phrasing and that kind of breathing together that the best quartets achieve, their playing had all the marks of greatness.

The Berg tends to dominate any program, not because of inherent greatness, but because it so vividly typifies the era of which it was a product, the Vienna of this century's first decade. Clearly a descendent -- nephew or niece? -- of "Transfigured Night" by Berg's mentor, Schoenberg, it is not yet the mature Berg that was soon to follow. But it is secure in form, tension-filled in its mastery of technical devices, and rich in the Tristanesque emotion that motivates every measure. The Tokyo foursome played it with awesome control and, where appropriate, a searing passion.

The Mozart quartet, first of the final three dedicated to the King of Prussia, has every reminder of the unbroken greatness Mozart poured out in his last years. It was played with an art that equaled the music.