Tomorrow evening at 8 o'clock in Sanders Theatre the Boston Symphony Orchestra will give its third concert of the season in Cambridge. With M. Plerre Monteux conducting, it will give Beethoven's Third Symphony, known as the "Eroica". Mr. Jean Bedetti, first 'cellist of the orchestra will give Haydn's Concerto in D Major. The concert will close with the suite from Ravel's Ballet, "Daphnis and Chloe".