Robert Mosley Jr. is a highly musical Porgy, while Michael V. Smartt focuses his energies more on theatrical values.

There will be two more Porgies on stage in the Kennedy Center Opera House during the eight-a-week performances running through June 18. Only time will show what each of them does with the role. But Smartt (in the first performance on Wednesday evening) and Mosley (in yesterday's matinee) showed that there is more than one valid way to play the crippled beggar.

Both spend the opera's three hours on their knees: Smartt moves across the stage, sometimes quite rapidly, on a four-wheeled dolly, but Mosley limps on his knees, which are protected by pads. There is a similar contrast in their singing and acting. Mosley's voice is heavier and richer and (at least this early in the run) it seems to cut through the orchestral sound with more verbal clarity. Smartt is more mercurial, closer to Broadway in his style. Perhaps that is why he was nominated for a Tony award during the show's run at Radio City Music Hall. Mosley may deserve a Tony, too, for pure musicianship--but how many people can you nominate from the same role in the same production?

The first two Besses, Henrietta Elizabeth Davis and Naomi Moody, were more alike. Both have fine voices and give essentially the same interpretation. As Clara, Luvenia Garner seemed a bit more secure than Janice T. Hutson in a few high notes of "Summertime," but this was a very small detail. Gregg Baker and George Robert Merritt were both impressively wild-bull macho in the role of Crown, and if Baker got his words across with more clarity and impact, it may be partly because his was the second performance of this production in the Kennedy Center Opera House.

The first two Washington performances show other significant differences. The show originally was conceived for a hall more than twice as large as the Opera House, and Wednesday night was the first time it had been performed without amplification. It was a night for adjusting to radically different performing conditions, and the problems of adjustment occasionally were evident in the presence or lack of verbal clarity, the balance of solo voices with orchestra and/or chorus, even the breadth of physical and musical gestures. A good operatic production is one that continues to grow after opening night, and the second performance confirmed emphatically that this is a good production.

While Porgies and Besses come and go, the stable identity of this production is entrusted in large measure to the chorus. This reflects accurately the nature of the opera. In fact, the real hero of "Porgy" is the chorus--the community, struggling to survive, to enjoy life once in a while, to protect its members, affirm its collective identity and perhaps move up a step or two on the American social ladder. When George Gershwin made a symphonic suite based on the music of "Porgy and Bess," he called it "Catfish Row." The same title might have worked for the opera itself, except that an aura of romance sells more tickets than an essay in pop sociology.

The recurring element in the opera's musical structure--in a way, its overall principle of musical and dramatic organization--is the antiphonal statement-and-response pattern of soloists and chorus, individual and community, which originated in Africa and still can be heard in the work songs and religious music of black Americans. A featured singer--usually Porgy, Bess, Crown or Sportin' Life--presents a proposition or precipitates a situation, and the community gives a choral reaction.

The pattern can be heard in its purest form in numbers that vary from the crap-shooting music in the opening scene to the fishermen's work song, "It Take a Long Pull to Get There." It is the essence of the religious music that recurs throughout the score. While its impact is less spectacular than that of a jazz-flavored novelty song like "It Ain't Necessarily So" or a soaring love duet like "Bess, You Is My Woman Now," this essentially African art form gives the work its basic texture and makes the chorus its true musical center. The chorus for this production is strong and superbly trained, with a fine ear for the music's richly varied idioms.

Among the secondary singers, Shirley Baines and Veronica Tyler were both excellent in the role of Serena. On opening night, Gwendolyn Shepherd, as Maria, was brilliant in her aria, "Struttin' Style," but not quite focused in her recitatives. Loretta Holkmann, yesterday, was a bit less spectacular but also less uneven. C. William Harwood conducted both performances well, the second somewhat better than first.