That often elusive quest for the truly American opera, devoid of European frills, made a big gain here Friday night with the first performance of "Harriet, the Woman Called Moses." Based on the life of Harriet Ross Tubman, the legendary "conductor" of the pre-Civil War Underground Railroad for runaway slaves, the opera is as unmistakably American in style as it is in substance.

All the more ironic, then, that it is the work of a Scottish composer, the eminent Thea Musgrave.

This is an opera with impact and, just as welcome, popular appeal. The opening-night audience at the Norfolk Center Theater responded with bravos from all sides.

"Harriet" is intensely dramatic, beautifully crafted and, at its best, eloquent. It is also a great credit to the 10-year-old Virginia Opera Association.

Doing an opera on Tubman was a grand idea, though it is based "very freely" on her life, in Musgrave's words. Tubman's life was certainly dramatic enough, after she fled from slavery in Eastern Shore Maryland and then returned at least 19 times, with a price on her head, to bring out more than 300 from bondage.

But Tubman is just the starting point for many of the work's finest moments. Musgrave turns "Harriet," especially in the long first act, into just as much of a profile of that eternally fascinating social phenomenon, antebellum plantation society. In this opera, the whites are treated with compassion and complexity as well as the blacks.

"Harriet" is a big opera in a physical as well as a sociological sense. The large chorus, or at least parts of it, is on stage most of the time. And those rich voices are intricately interwoven with a considerable number of solo parts and the sometimes diaphanous, sometimes "Boris"-like orchestral line. It is the orchestra, in fact, that not only glues this multitude of scenes, arias and ensembles together but also most maintains the consistent mood of harmonic ambivalence and, at the right moments, foreboding.

Knowing beforehand that the music would be full of quotes from the most familiar spirituals, one feared they would sound like gimmicks, giving an inaccessible work a popular edge. On the contrary, they are sometimes used with a subtlety bordering on leitmotif.

"Harriet" remains, though, an uneven work. The first act is basically better focused than the second, because it is organized around individual relationships and the musical ways of expressing them. Thus this act produces set pieces of great beauty -- the first love duet between Harriet and her lover Josiah; her lullaby as she rocks the white child of the wastrel Preston (nicely sung by Barry Craft); and the whole thrilling end of the movement as Harriet decides to set upon her dangerous and daring course, ending in some beautiful singing in the high soprano register.

The second act, which is shorter, tends to focus more on events than relationships, and thus is musically less clearly focused and developed. There are several magic moments, though -- especially the song of Harriet's mother, Rit, sung so beautifully in the big voice of Alteouise DeVaughn.

The end of the opera, in which Josiah (sung and acted with great force by Ben Holt) is shot as he and Harriet are escaping across a bridge into Canada, still needs work. Another problem, as in much modern opera, is the tendency to fall into sterile declamation when exposition of the plot is being expressed.

Soprano Cynthia Haymon performed the title role on crutches after she fractured an ankle in rehearsal. No doubt this robbed Hayman of a considerable amount of the force that she could have brought to the role, yet it made the heroine's courage all the more poignant.

Harriet's father, Ben, was movingly acted and sung by Raymond Bazemore, and there was not a serious weakness in the whole large cast.