There was a time, not too long ago, when the world of opera was dominated by singers. Now it is the director who is cock of the walk in opera houses. More and more, opera as a vocal medium gives place to opera as a theatrical event. This could be a good thing if the director really cared about music and the integrity of the work at hand - Franco Zeffirelli and Piero Faggioni come instantly to mind. But nowadays, directors seem more intent on leaving a personal stamp on every work - enshrining new visual graffiti that are about as appealing and artistically satisfying as the so-called street art of the New York subway trains.
A prime example of this not-so-new but terribly aggressive style is to be seen in the Metropolitan Opera's first staging of Mozart's ''La Clemenza di Tito ,'' directed by Jean-Pierre Ponnelle, who also served as designer. The crumbling-pillar proscenium-type unit first seen in Ponnelle's staging of Mozart's ''Idomeneo'' two seasons back is again used - gone are most of the seashells (a few starfish and clumps of algae notwithstanding) and added are myriad balconies and doors meant to evoke a Baroque vision of imperial Rome. While impressive visually, it is cumbersome, and it overpowers this opera.
Perhaps Ponnelle realized the sets were too massive and tried to compensate with action, for action is the crux of this ''Tito'' - action and costumes. Characters are dressed for effect and are moved principally to create motion. Hardly a moment goes by without some frenetic activity, generally created and imposed on a situation that often begs for the unique focus that only stillness brings.
Many of Ponnelle's devices worked in the aforementioned ''Idomeneo.'' Few of them work here. The climactic aria for Vitellia, ''Non piu di fiori,'' is staged as a flat-out mad scene, as was Elettra's ''D'Oreste e d'Aiace'' in ''Idomeneo.'' Here Renata Scotto twirls around, falls to the floor, even hugs the prompter's box while making grotesque, assumedly demented faces. At more than one moment her actions - directed for camp value rather than for dramatic effect - were greeted with hoots of inappropriate but unavoidable laughter.
Miss Scotto was returning to a Mozart opera after a separation of 20 years. Although a few moments offered her vocal troubles of the squally kind, she nevertheless gave the only true performance on stage at the premiere. In the ''Non piu di fiori,'' she was riveting, dramatically and musically. Her way with recitatives was electrifying, full of meaning and superb in matters of enunciation, as is always the case in her portrayals.
The rest of the cast was on a conspicuously lower level vocally. Kenneth Riegel was, somehow, cast in the title role, and he was simply not up to the demands of the evening. Irish mezzo Ann Murray, who was to debut as Annio, stood in for an indisposed Tatiana Troyanos in the pivotal role of Sesto. She scored a huge triumph with the audience and sang the role honorably under the circumstances. The voice, however, lacked amplitude and tonal quality at each extreme of the range. Ariel Bybee was the effortful Annio, Gail Robinson a bland Servilia, and John Cheek the neutral Publio. In the pit, James Levine's performance grew in energy and nuance as the evening progressed.
Mr. Ponnelle is not the only motion-motivated director opera sees these days. Frank Corsaro - as witnessed in his staging of that popular double bill ''Cavalleria Rusticana'' and ''I Pagliacci'' at the New York City Opera - also insists on filling the stage with frantic activity and an effulgence of props, statues, and extraneous characters. In every instance, the ideas intrude on the drama and consistently draw focus away from the singers.
Those singers also had to fight a conductor - Klaus Weise - whose ideas of tempo, particularly in the ''Pagliacci,'' evoked leisurely Wagner rather than verismo Italian opera. The best singers managed to hold their own despite all the handicaps. Nancy Shade lacked the strong top notes for Santuzza, but she made a vivid impression, nonetheless, as did Alteouise DeVaughn as Lola.
In the ''Pagliacci,'' Marianna Christos sang a sumptuous Nedda, and Jon Fredric West gave us a ringing, impassioned Canio that was marred only by some odd breaths before high notes and a tendency to revert to old-fashioned histrionics.
The best side of City Opera productions is still to be seen in Tito Capobianco's dynamic production of Boito's ''Mefistofele,'' starring the incomparable Samuel Ramey. Mr. Ramey's Mefistofele is one of the great stage impersonations of the day. Quite apart from the sheer visceral impact of his physical and vocal presence, all the visual trickery and stage effects combine to showcase a superior performance like Ramey's. It is, on every level, a triumphant production, handsome in sets (David Mitchell), costumes (Hal George), and lighting (by the late Hans Sondheimer, to whose memory this run is dedicated). It accentuates the music, gives the aural experience a visual counterpart, and is, from beginning to end, superbly theatrical.