As Benjamin Britten's opera "Billy Budd" is a unique achievement in the composer's long list of successful operas, so is its production one of the finest accomplishments in the history of the Metropolitan Opera.

Seen at the Kennedy Center on Saturday night as the closing offering of a week of Metropolitan performances, "Billy Budd" is a remarkable tribute to the strengths of the entire company. The all-male cast presents a series of individually etched portraits of Melville's characters that are given remarkable personalities and strong musical profiles by the members of the Met's family. It would be a serious injustice not to mention them by name:

David Ward's Mr. Flint; Morley Meredith as the Bosun; John Darrenkemp's Donald (not forgetting his notable Montano in "Otello"); Michael Best as the offstage Maintop; James Atherton's touching Novice, and his equally affecting friend, John Davies; Andrea Veils as Squeak; Peter Glossop as a notable Mr. Redburn; Julien Robbins outstanding as Lt. Ratcliffe; Robert Nagy singing Whiskers; Nico Castel as Jones, and Andrew Foldi memorable as Dansker. As for young Matthew McGrath, the cabin boy, he has a future. In addition to those, the men's choral singing is powerful and eloquent.

The opera triumphs through Britten's feeling for the basic conflict between good and evil and his unerring gnius in the use of tone colors, from orchestra and voices alike, in painting moods.

Every aspect of male vocal texture is exploited, with a brightening of the sound by the use of of a quartet of boys' voices. In the orchestra, the unforgettable series of chords that is passed around the orchestra, from brass to woodwinds to strings, while Captain Vere is holding his final, fateful conversation with Billy, is one of Britten's strokes of genius.

The principal roles of Billy, Claggart, and Captain Vere are differentiated in every conceivable manner. These were effectively handled on Saturday by Richard Stilwell, whose look as the fated Billy is the personification of good, as James Morris, in tone, bearing and even vocal production, typifies all that is evil in Claggart.

Richard Cassilly won solid applause for his Captain Vere. Despite an unattractive sound, he sang the role with conviction, without effacing the indelible memory of Peter Pears in the same part with the same company.

Raymond Leppard conducts the score with absolute awareness, command of every nuance of meaning, while drawing out of each performer onstage and in the pit the finest results. The Met has polished and refined what was a distinguished performance of "Billy Budd" into a magnificent artistic totality.

On Saturday afternoon, "Hansel and Gretel" was sensitively sung by Brenda Boozer and Gail Robinson in the title roles with Allan Monk and Jean Kraft strongly supporting them as their parents.

The production looks fetching, with irresistable mushrooms, bats, elves, a spider and a witch who rides through the air in a broom. Andrea Velis sings the Witch these days. It is no reflection on his gifts that a great contralto still seems preferable.

Neither Loretta Di Franco nor Louise Wohlafka made their scenes as Sandman and Dew Fairy the true gems that Humperdinck created, but they were not given much encouragement in that direction by Calvin Simmons, whose square conducting encouraged the orchestra to sound coarse and scratchy. It was hard to believe these were the same musicians who were so great on Saturday night.