Welsh Opera's `Falstaff'. The Welsh National Opera relies on excellence in acting and directing - though sometimes at the expense of the music. MUSIC: REVIEW

THE Welsh National Opera presentation of Verdi's ``Falstaff'' - seen at the Brooklyn Academy of Music recently in the third of four performances - prompts the question: ``Can opera survive on purely theatrical and orchestral excellence when the voices are mediocre?'' The answer is hardly a categorical ``No!'' But the Verdian pleasures we could glean from Peter Stein's highly acclaimed staging and Richard Armstrong's deft conducting of the impressive Welsh National Opera orchestra were compromised by singing that can only be described as bleak.

The opera's managing director, Brian McMaster, was faced with a dilemma when he came to the company in 1976: He didn't have the budget for star singers and knew he would have to find an alternative to voice-oriented performances.

So Mr. McMaster turned to Europe's most notable theater directors, offering them something unusual in the opera world - an ensemble company of acting singers, and abundant rehearsal time.

Because the company tours extensively, productions have a good run. This ``Falstaff,'' for instance, was played 19 times before crossing the Atlantic by way of a run at the Royal Opera House, Covent Garden.

I found Mr. Stein's approach to ``Falstaff'' refreshing. Founder of Schaub"uhne, West Berlin's most noteworthy experimental theater troupe, he takes a decidedly traditional view of the work. He effectively and effortlessly achieves an illumination of scenes, of personal interactions, and of the linear nature of the story line adapted from Shakespeare. People move with grace. Though their action is choreographed, the execution is so smooth that it seems natural and spontaneous.

Unfortunately, this often superb staging frequently took place on unsightly sets: Lucio Fanti may have tried to depict an Elizabethan sensibility, but his minimalist orange and black Tudor designs didn't suggest much of anything. Moidele Bickel's costumes were fine for the men but rather too general in feeling for the women.

Yet at times, Stein's work was so remarkable one could almost forget the sets. For instance, I have never seen the pandemonium of the second act finale better managed - with all the men searching for Falstaff and Alice Ford, while the women are trying to keep the portly knight hidden in a too-small laundry basket and Nanetta and Fenton are smooching behind a screen. At each moment we were always unobtrusively guided to focus on the pivotal person or action.

And when Sir John was finally dumped into the river with the dirty laundry, the action was preceded by a momentary pause that allowed us to see the incongruity of this corpulent man's plight. We witnessed his helplessness and shock at the nasty tumble he was about to take, and we actually noted how each character was reacting. Stein managed this ``freeze frame'' moment with barely a perceptible pause.

Verdi's fugal finale was performed with a real sense of the music and text being translated into action and interaction.

The women had an especially natural sense of camaraderie, aware that, in the prefeminist game of life, knowing the rules so you know how to bend them was the only way to survive. And since these men are rather like lemmings, following this call or that to hurl themselves into melees or just plain chaos, the women's often ironic manner was all the more believable and human.

I could have done without the manic action for Nanetta in the second act - which looked more like Cassandra imploring the unheeding Trojans than a girl unhappy in love. And I could not fathom what Stein was after with his characterization of Mistress Quickly, who looked and acted like a reject from a bargain-basement ``Carmen'' set in San Francisco's Haight-Ashbury district 25 years ago.

All this brings us to the singing itself. Verdi's last opera has no arias, but this doesn't mean he expected it to be poorly sung.

Arguably the best voice of the evening belonged to Suzanne Murphy as Alice Ford. Hers was a truly radiant stage presence, yet she used her sizable soprano unevenly and often harshly.

The Falstaff, Robert Maxwell, has that sort of bright, serviceable baritone that would hold a regional company in good stead. When he was paying consistent attention to his stage gait (the most variable part of his performance), his Falstaff had an engaging, if too knowingly foolish, presence.

David Malis was a vocally disappointing Ford - solid, with no real amplitude in the high notes - but his acting was as strong as could be.

Soprano Nuccia Focile as Nanetta and tenor David Owen as Fenton both ran into troubles during their major moment together in the last scene. The secondary performers were consistently better histrionically than vocally.

The Brooklyn Academy of Music opera series is dedicated to bringing unusual stagings to the New York area - a much-needed alternative to the often oppressive conservatism of the city's two major opera houses, the Met and the New York City Opera. The next production will be ``Das Kleine Mahagonny,'' Peter Sellars's curious blend of excerpts from Weill's ``The Rise and Fall of the House of Mahagonny'' and from Bach cantatas (March 30-April 2); followed by an acclaimed production of Lully's ``Atys,'' with Les Arts Florissants and conductor William Christie (May 17 and 19-21).