THEY WERE YOUNG and rather average looking. Three men, three women. Only one among them had a well-trained singing voice. Sweat-stained backs and armpits. And when they finished singing and sweating they slid off the stage and into the audience.

Some mingles later they were gone and the audience filed out into the street. They left without autographs or cast albums, without any catchy show tunes on their breath. No sound or sight or smell distinguished them from the rest of the night-lifers stolling along the asphalt and concrete called Tremont and Boylston. Except they knew and felt, and maybe even almost smelt, more of that hidden earth below than anyone this side of Fenway Park.

Nightclub Cantata is the title director Elizabeth Swados has given to the 75 minutes of theatre that had just put actors and audience back in touch with their world--not just beneath but above, and even within, themselves. The location has since changed to the Charles Playhouse and the off-Broadway cast will soon be replaced, but Cantata is a hit that likely won't leave Boston soon.

Swados has created, composed and directed 21 musical numbers--each a separate attempt to explore the many levels of human interaction through simple song and melody. Nightclub Cantata is part of her search for "new words for music," words, she says, "that will not make either bad poetry or easy emotions." Playing with a vast range of 'foreign' languages, she has set to music "Avesta," an old Persian cursing language, as well as jungle choruses and a bird lament.

Swados finds the simplest statement of her theme in two works of Nazim Hikmet. "Things I Didn't Know I Loved" opens Cantata, celebrating an adult re-awakening to the fundamental miracle of life bursting with questions for animals and astronauts alike. "On Living" ends the show with a return to general statements on existence: "Living must be your whole occupation... Plant olives at seventy and not for your children... We must live as if one never dies."

Swados calls upon Pablo Neruda, Sylvia Plath, Frank O'Hara, and others, including herself, to provide the words that fall in between the two Hikmet pieces. Often these sources point out the manner in which language not only expresses but also defines the way we treat each other.

For example, "Isabella" is about the "camp language" of Auschwitz. Isabella understands it no more than her French or Hungarian fellow prisoners. The words are German and so is she. But the words stand for ideas that "not even God can understand." Gas chambers. Extermination. Yet Isabella survives. "Suffering doesn't kill you," she sings, "only death."

The rest of the evening is much lighter than "Isabella," though no less intense. Swados selected the pieces from her workshop at the Lenox Arts Center without enough alteration to properly fit the stage. Numbers like "Bestiario" and "Dibarti" are merely actors' exercises, delivered with spitspewing intensity. Successful theatre must rely on something more and something less than shouting to move and involve its audience.

Swados also has not overcome the problem of integrating into a whole the varied subjects and formats of the adopted pieces. Blackouts are used too frequently for transition between numbers instead of more refined staging and lighting. At times the structure disappears, turning Nightclub Cantata into Up With People gone disco.

Within this sometimes flimsy framework some numbers are strong enough to stand on their own. In "Bird Lament" a woman sings of the sadness of a bird, bringing herself and the audience to the point of tears without any movement or human language. "Are You With Me" is a beautiful blues number, a duet for voice and piano about committment in love. The most exciting song is "The Dance," a rousing gypsy song that slides back and forth from an intellectual consideration of an existential decision to the simply joy of experiencing the alternatives through stillness and movement: "If the choice is to sit in the sand or dance, why not dance?"

WOMEN ARE the center of these three pieces and women are the strength of Nightclub Cantata. This is not women's theatre, however, and the less impressive men fill half the cast and almost half the script. The fault lies mainly with the script, for the male parts are mostly restricted to humorous numbers which belittle but do not develop character. The men fade into the background, unable to fit the roles of strength and love the women desire for them.

Ignoring the issue of the general strength or weakness of the male characters, it is still difficult to understand why Swados has included many of the show's comic sketches. The Flying Pastrami Brothers are an amusing comment on the overly proud and pompous trapeze artists of the circus, but they add nothing significant to Swados' ideas about attitudes towards life. The routine between a ventriloquist and his dummy is not even funny, stoien as it is from a common vaudeville act.

There are, however, some humorous numbers which do more than amuse. "Indecision" is a fifties satire with the show's best staging and a song that's got, you know, a beat. It is a song about adolescent anxiety that helps connect a preceding piece on children with later numbers about more permanent relationships. "Albatross Ramble" floats from comedy to tragedy and back as it examines the burdens that life dumps in our laps.

The comic songs are all accompanied by well-conceived staging, while the more serious numbers seem visually limp and clumsy. Perhaps this is just another holdover from the original exercises, in which Swados presumably sought to work exclusively through music and words. Whatever the reason, the non-verbal expression, both facial and anatomical, is far too limited.

Still, it works. In the end the cabaret style that causes Swados so much difficulty also saves her. The weak points fade into the blackouts, while the mood keeps building with each successive piece. The music--calypso, raga, and jazz tunes especially--dull the overly critical senses with their inebriating optimism. You have to smile after Nightclub Cantata. You have a stringer full of speckled trout on a sunny day. Who cares about the big one that got away?