Scott Joplin's opera, "Treemonisha," holds a tantalizing promise, largely unfulfilled. It was published during the composer's lifetime (at his own expense), but it did not reach the stage -- at Wolf Trap in 1972 -- until 55 years after his death. If it had succeeded during his lifetime, Joplin would certainly have written other, even better operas. He was at work on a symphony when he died.

In the '70s, "Treemonisha" was an enormous success -- thanks largely to the lavish Houston Grand Opera production of 1975, which will be telecast on PBS this weekend (10 tonight, Channel 26; 10 tomorrow night, Channel 32.) It is now recognized as a landmark in the history of American musical theater. But Joplin's life was shortened by the exertions and frustrations of his unsuccessful attempt to get it produced and to win recognition as a classical composer.

He deserved that recognition; if Chopin's Mazurkas are classical music, so are Joplin's rags. But he was unable to break through the stereotyped thinking of his time, which put black musicians and classical music into two separate, noncommunicating worlds.

Considered objectively today, "Treemonisha" seems musically and theatrically as promising as the first operas of Mozart, Verdi, Wagner or Puccini. Like them, it is apprentice work, heavily indebted to the conventions and traditions of its time. But it also shows, again and again, sparks of true, fresh inspiration. The primary difference is that the other composers developed their talent in a context where the writing of operas was something expected of them and encouraged. They went on from their first efforts; Joplin was stopped in his tracks.

"Treemonisha's" weaknesses are not musical. They are derived from the fact that Joplin wrote his own libretto -- and even in this department, he did not fall far below the usual level of his time.

The plot, dealing with the struggles of a young schoolteacher against a drug dealer in the era right after Emancipation, is rather simple and the potentials for suspense and dramatic tension are by no means fully exploited. In addition, the lyrics often fall into preachiness; "Treemonisha" is sometimes artistically a victim of its own good intentions.

But as opera librettos go, it is not bad. It gives an imaginative director plenty of opportunities for striking stage effects, and these advantages are thoroughly exploited in the Houston production.

Musically, "Treemonisha" is a delight. In the big vocal numbers, Joplin shows a thorough knowledge of the potentials of the singing voice, and the dance numbers are spectacularly fine, enhanced in this production by adept choreography and a skilled, energetic corps of dancers.

Like the dances, the most memorable vocal numbers are in Joplin's familiar and delectable ragtime style, but he also echoes the rich black heritage of spirituals and work songs and even the special style of the barbershop quartet. The music is often inspired and never less than highly competent. It is generally well-sung, with particularly distinguished work by Carmen Balthrop and Curtis Rayam in the leading roles.

The Houston production's video edition does "Treemonisha" full justice in ways that were not available to the audio recording issued by Deutsche Grammophon. A large part of this production's appeal lies in the colorful costumes, striking scenic details and inventive dance routines. It might have even more impact if it were taped with today's advanced techniques rather than the more primitive treatment of a decade ago. But this "Treemonisha" is a skilled, imaginative treatment of an attractive work of art.