Brahms and the Cleveland Orchestra got off to a rousing start Saturday night in the Kennedy Center. Under the direction of Lorin Maazel, the Ohio visitors will be there this week, playing all the Brahms symphonies, concertos, overtures, and the Requiem, plus one serenade and the Haydn Variations. Isaac Stern was soloist in the violin concerto at the opening concert.

The orchestra is just back from a series of concerts in Mexico where they enjoyed nightly standing ovations, a habit Saturday night's wildly enthusiastic audience did nothing to discourage. And there was enough to applaud.

Brahm's orchestral writing is continously marked with a rich warmth of sound, heightened at times by the brilliance of brass outpourings that many audiences love more than almost any other repertoire. The Cleveland Orchestra was, under George Szell, for many years one of the world's supreme Brahms ensembles.

On Saturday it exhibited much of the lustrous tone for which it has been famous. The strings and woodwinds were especially mellow most of the time. The brass, however, both in trumpets and horns, often took on an unwanted edge in loud passages that came close to raw, unbalancing the best efforts of their colleagues.

Stern is one of the world's great players of the Brahms concerto in which his track record yields to none. On Saturday he, Maazel, and the orchestra, especially the cellos, engaged in dialogues of intimate beauty that were remarkable. John Mack's oboe, too, in the famous solo, was worth the special attention he received when it was over.

That there were some stray notes from the violin was of no great matter in light of the high mood of most of the playing.

The Academic Festival Overture began things with fine spirit, if a bit raucously in the brass. Maazel taking the last page unusually slowly. It was in this area of tempos that he really got into bad habits in the First Symphony.

Brahms knew as well as the next composer just how to indicate a ritard or a speeding up. Nowhere in the First Symphony does he ask for a ritard. He does in the second, twice, and three times each, which is extremely sparingly, in the third and fourth symphonies.

From Maazel's willful waywardness in tempos on Saturday, you would have thought Brahms had scattered request for ritards every few pages. They are distressing in Maazel's readings, coming so often on the last beats of measures, interrupting the normal flow of the music. At times, as in the great horn calls at letter M in the finale, they are gross distortions.

The worst moment of all came at the final chorale of the finalewhen Maazel took the big, old-fashioned slowdown that has long been abandoned by better musicians and which Brahms himself strictly forbade. IT sorely marred what had already become a distressing reading.

On Sunday night, Maazel played just two works by Brahms - two of the greatest - and the evening was largely a triumph.

Rudolf Firkusny was soloist in the D Minor, the first of the piano concertos. He helped mightily to make the performance great in all aspects. With conductor and soloist seemingly at one in interlocking disciplines, the rugged peaks of the concerto were outlined in all their immensity while its poetic vistas were exquisitely molded.

Firkusny worked wonders with the pedal to keep the heavy bass passages clear, while at the other end of the keyboard his tone was a thing of singing luster, again with magical kinds of pedaling. For the largest moments, he drew upon a huge reservoir of sound, never forcing a note.

Maazel seconded him masterfully at every moment. No wonder the concerto was thoroughly superb. Incidentally, for this engagement, Firkusny flew up from Fort Worth where he is one of the judges in the current Cliburn Competition where the rivalry is better than ever.

In the Second Symphony Maazel conducted with a lyric touch of fine relaxation, keeping for the most part very close to the directions in the score. It was an account of eloquent beauty.