That often elusive quest for the truly American opera, devoid of European frills, made a big gain here tonight, 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. Tonight's audience at the Norfolk Center Theater -- which included many luminaries of the international music world as well as such pillars of the Virginia establishment as Gov. Charles Robb and former governor Mills E. Godwin Jr. -- 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 toward the North Star from slavery in Eastern Shore Maryland and then returned at least 19 times to bring out more than 300 from bondage. During that period there was at one point a $40,000 price, "dead or alive," on the head of this most celebrated member of the Underground Railroad.

Tubman, though, 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 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.

Her 10th opera, and the first on an American subject, "Harriet" resulted in part, Musgrave says, from a fascination with the timbres of black voices that began with a Virginia Opera production of "Porgy and Bess" several years ago. (Musgrave lives here and her husband Peter Mark runs the company.)

"Harriet" is not even remotely as melodic as "Porgy," but it shares with Gershwin's work a sociological depth -- in the sense that "Porgy" is as much about all of Catfish Row as it is about the title characters.

"Harriet" is also a big opera in the physical 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 (some of them very meaty ones) 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 -- the transitions are wonderfully deft -- but also most maintains the consistent mood of harmonic ambivalence and, at the right moments, foreboding. Musgrave is a formidable orchestrator.

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

The work marks, particularly, a new direction in compositional style for the 56-year-old Musgrave, who has written in everything from sweet lyricism to asynchronous music, in which each note is notated but need not be exactly coordinated with the others.

"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; and the whole thrilling end of the movement as Harriet decides to set upon her dangerous and daring course, ending in some beautiful high 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. It was the only time that the performance was interrupted in mid-act by an ovation.

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, and it is clear from some of the notes in the program that it has been getting a lot of it.

Another problem, as in much modern opera, is the tendency to fall into sterile declamation when exposition of the plot is being expressed. That made the quarrel between the decent master (Jay Willoughby) and Preston over gambling debts uninvolving. Verdi would have done it better.

An unscheduled dramatic element was the performance by 26-year-old soprano Cynthia Haymon in the title role, on crutches after fracturing an ankle in a recent rehearsal. This was a tremendous handicap, because Harriet is nothing if not mobile as she thunders through her crusading life. No doubt this robbed Hayman of a considerable amount of the force that she could have brought to the role, yet one suspects that some of the fragility of her characterization of Harriet would have been there anyway. It made the heroine's courage all the more poignant.

Haymon has a beautiful voice, which she used with considerable sensitivity to the vocal lines and to the high sonorities that Musgrave has built into the part.

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

The director was Gordon Davidson, of Los Angeles' Mark Taper Theater and the man who directed "Mass" at the opening of the Kennedy Center. He does wonders in keeping the scenes moving in this fast-paced drama. One of the reasons that the end is a bit of a problem is that the quite handsome unit set just doesn't lend itself to resembling a bridge -- no doubt Davidson will work that out along with set designer Jeffrey Beecroft.

The next stop for "Harriet" is at one of the world's most prestigious houses, Royal Opera, Covent Garden, which co-commissioned the work. This opera has such broad appeal, especially if more work is done on some of its lesser moments, that it would behoove a number of other institutions, including the Kennedy Center, to start perusing it right now.