This double bill in Opera Unlimited's festival of chamber operas is a powerhouse evening of musical theater -- first-rate performances of exciting works by John Harbison and Elena Ruehr.

The world premiere of Ruehr's ''Toussaint Before the Spirits'' had the audience on its feet, cheering, whistling, and applauding for the work, the composer, and the astounding performance of baritone Stephen Salters as the Haitian patriot Toussaint L'Ouverture. The libretto is by Ruehr herself, Elizabeth Spires, and Madison Smartt Bell, whose novel about Toussaint, ''All Souls' Rising,'' inspired the composer; the text depicts Toussaint, betrayed by Napoleon, in the hours before his death in a freezing French prison.

Ruehr's music combines a lyrical outpouring energized by motor rhythms that never become mechanical. Harmony, rhythm, and melody interact and surprise. She knows how to write for singers and how to assimilate forms and styles into her own compositional voice. You can hear many influences in the piece -- minimalism, neoromanticism, African and Haitian rhythms, period touches (the opening evokes Bach's ''Italian Concerto''), even, at the end, a Broadway anthem about the ''Tree of Liberty'' -- but it all holds together.

The opera begins with a conversation between the prison governor and Toussaint that's comparable to the one between Captain Vere and Billy Budd that Benjamin Britten left off-stage in his operatic adaptation of Melville's famous fable; then it moves to a different genre. Toussaint is left alone with the spirits from his African/Haitian culture, the voices of his past, and his ideals, and the work becomes a dance-opera about self-realization. The form takes us back to the beginnings of the art, and to one of the first great operas, Gluck's ''Orfeo,'' where Orfeo subdues the dancing Furies with his singing. Here the Spirits make Toussaint whole.

Ruehr's music may lack repose, but it is compelling, emotional, theatrical. And Salters goes all out as singer, dancer, and actor; he's a fearless and exhaustingly honest performer and a thrilling singer. The choreography by Nicola Hawkins mingles angular movement with an eerie legato style in which it seems the six dancers are moving through some element other than air; there are Katherine Dunham-style ethnic aspects, too. There are remarkable performances by William Hite as the prison governor, Ramone Diggs as Toussaint's rebellious adopted nephew, and Alison Buchanan as the spirit medium. Not to mention the work of the chamber orchestra under the skilled and committed direction of Gil Rose. The success of ''Toussaint'' clearly marks a point of arrival for Ruehr, and also, we must hope, a point of departure.

That's what ''A Full Moon in March'' represented for Harbison, who was 37 when the Boston Musica Viva premiered it back in 1977 -- it was one of his first fully realized works and a masterpiece of the chamber-opera genre, and it led to many other things. The text is a ritual drama by the Irish poet W. B. Yeats, mingling Japanese models with European commedia dell'arte influences, a tale about a queen and a swineherd that combines unsavory elements of the myths of Turandot and Salome; this is surrounded by a strange commentary by two ''attendants'' that is partly satirical, partly not.

The writing burns like dry ice; it is assured, colorful, unfailingly inventive, and often mysteriously beautiful. A doctored piano provides a gamelan effect, and the bass clarinet (Gary Gorczyca) is virtually a character in the drama. Lynn Torgove's staging was both precise and evocative, and there were superb performances by Frank Kelley as the Second Attendant and James Maddalena as the Swineherd; Lorraine DiSimone and Anne Harley were satisfying as the Queen and the First Attendant. Hawkins was a baleful presence as the dancing Queen who kisses the severed head of the Swineherd. Rose again was a persuasive presiding spirit.

An evening of music theater like this tells us how extraordinary the city's artistic resources are, and what our opera companies could become, if they only wanted to.

A Full Moon in March Opera by John Harbison Toussaint Before the Spirits Dance-opera by Elena Ruehr, presented by Opera Unlimited At the Massachusetts College of Art Saturday night (repeats tonight).

This story ran on page D1 of the Boston Globe on 6/10/2003.

© Copyright 2003 Globe Newspaper Company.

© Copyright 2003 New York Times Company. Reprinted from The Boston Globe, Living / Arts, of June 10, 2003.