As an adaptation of Shakespeare, Wagner's youthful opera "Das Liebesverbot" ("The Ban on Love"--based on "Measure for Measure") does not rank anywhere near Verdi's "Otello" or "Falstaff."

But as an opera it is certainly equal to many in the active repertoire. Saturday night, for one performance only, it had its American premiere at a music festival in Waterloo Village, N.J.--147 years after its first performance in Magdeburg, Germany, and a full century after the composer's death.

The performance, in concert form, did not do full justice to the work as a theatrical experience, but it gave considerable musical satisfaction, it offered a fascinating glimpse of a young composer testing his talent before choosing his final, unique style, and it served as a first-class showcase for a major new talent: Alessandra Marc, a young Washington soprano who took a secondary role and stole the show.

Verdi toyed with Shakespeare through most of his career before producing his two final masterpieces at an age when he thought he had finished composing. Wagner did the opposite: he composed, produced and conducted his only Shakespeare opera (and his only comic opera except for "Die Meistersinger") at age 22 in a style closely allied to the bel canto manner fashionable in the 1830s. "Das Liebesverbot" might have held the stage, despite its contrast to the composer's mature style, but Wagner later came to despise it. In an inscription on a copy of the score presented to King Ludwig II of Bavaria in 1866, 30 years after its premiere, he called it a "sin of youth" and said he had "erred" in composing it. His composition of this work was closely linked to his ardent pursuit of Minna Planer, a member of the Magdeburg opera company who would become the first Mrs. Wagner. In later years, he lost interest both in the opera and in the woman who inspired it.

"Measure for Measure" is a problematic comedy--a dark, brooding study of those eminently Wagnerian themes, love and death. As his own librettist, Wagner simplified the original (a common occurrence when a spoken play becomes an opera) and moved its locale from Vienna to Sicily, an Italian society under German rule, so he could point up the contrasts between Italian spontaneity and Germanic legalism and rigidity. At that time (though his attitude changed drastically later), he was on the side of the Italians--partly because he did not feel that the German operatic establishment had shown sufficient respect for his genius. In his memoirs he described the opera's themes, accurately enough, as "opposition to puritanism and hypocrisy . . . bold glorification of sensuality."

The plot turns on a decree banning wine, women and song (or, more precisely, the celebration of Carnival, fornication and drunkenness) with a death penalty for transgressors. The first victim chosen to be an example under this law is Claudio, who has got his mistress with child in Shakespeare, though Wagner, writing in a more puritanical atmosphere, is less explicit. Claudio's sister Isabella, who is about to take the veil in a cloistered order of nuns, leaves the convent to straighten out the situation and does so by involving the German governor, Friedrich, in a compromising situation with a woman who turns out to be, embarrassingly, Mariana, his own abandoned wife.

Despite the Italian sympathies he shows in his plot development and melodic cadences, Wagner's German character emerges in the solidity of his forms, the richness of his orchestration and occasionally in his habit of lingering too long in the overture or a vocal ensemble, elaborating it musically at the cost of dramatic effectiveness. Still, "Das Liebesverbot" is a thoroughly engaging composition--on one level, a striking tribute to the power of Eros; on another, a beguilingly complicated comedy. Along with the bel canto melodies, there are some passages of striking dramatic power--notably the confrontation of Isabella and Friedrich in Act I, Scene III--and occasional glimpses of Wagner's later style. Some of the music was actually adapted for use in "Tannhau ser," where it fits in quite readily. Given a good, singable English translation and a catchy title such as "Forbidden Love," it might find an audience in this country.

For the American premiere, Gerard Schwarz conducted a bright, well-paced performance that could have profited from a bit more rehearsal but worked well enough in a festival setting. Tenor Donald Grobe of Berlin's Deutsche Oper, probably the best-known singer in the cast, began with his voice not quite warmed up but later settled down to produce some superb singing. Distinguished work was also done by Roger Roloff as Friedrich, Jeanne Distell as Isabella, Edward Crafts as Brighella and Howard Hensel as Claudio.

But Alessandra Marc, in the role of Mariana, produced a sensation, beginning in the exquisite soprano duet of Act I, Scene II, and climaxing her performance with a superb aria in the final scene. Hers is a big voice, deep and rich in tone but very flexible and subtle in emotional nuances. If she can overcome a rather serious weight problem, the sky may be the limit for this superb young voice. All the singers were warmly applauded at the end, but she received and deserved a five-minute standing ovation.