Presenting The Barber of Seville and The Marriage of Figaro on successive evenings not only gives the New England Opera Theater a repertoire of two standard works, it enables audiences to follow Beaumarchais' drama from the Count's frivolous courtship of Rosina through their tragi-comic marriage. Rossini's music for the first play perfectly reflects its brittle stylized comedy. And the score of Mozart's "sequel" (actually written thirty years earlier) given to the older characters an almost bitter-sweet maturity.

Boris Goldovsky directs the Opera Theater's productions in a unique manner. With loudspeakers amplifying the orchestral sound onstage, his singers know the music so well that they rarely have to watch the conductor. Consequently, the staging has the flexibility and coherence often lacking in opera. Another important concession to dramatic values is the use of translations. English does not lend itself really well to the rapid-fire arias of Bartolo and Figaro, but in recitatives it becomes invaluable for following nuances of the plot. Apart from the language change, Mr. Goldovsky adheres to the composer's intentions. Rosina, for instance, is sung by a mezzo-soprano as Rossini first planned. And she sings his original Lesson Scene, not the customary aria interpolated for benefit for the claque. The orchestra is authentically chamber-size and the theater itself much more intimate than our standard operatic caverns.

Mr. Goldovsky's approach and the intensive rehearsal it entails have produced the sense of ensemble in his singers that is important for Rossini and crucial for Mozart. The second act finales in particular present unified vocal groups and not-as at the Metropolitan-a few soloists who happen to be singing simultaneously.

All the Opera Theater's singers are competent, and some considerably better. Mac Morgan, James Joyce, and Robert Mesrobian sing and act The Barber with magnificent style; Adele Addision's Countess combines a marked dramatic talent with vocal beauty that is easily outstanding among American sopranos.

Since the Rossini work has been on tour since last year, it runs with amazing case and pace. The Marriage production, still new, has not yet acquired the same polish, but both provide evenings of operatic charm all too rare in Boston.