AS great opera singers reach their mature years - which in the athletic world of opera singing means 50 and beyond - most tend to consolidate their work, to focus on the roles for which they are best suited. For an opera singer, the sixth decade of life is not a time to be taking chances.
But then there is Placido Domingo, who turns 54 in January and, by critical consensus, is now doing some of the finest singing of his career. Of course, you wouldn't know this from watching ``The Three Tenors,'' that shameless display of tenorial combat and synchronized mugging. Mr. Domingo can safely have fun and make money, however. (He, Luciano Pavarotti, and Jose Carreras reportedly earned $1.5 million each for the last concert.) Because of his other activities, his reputation as a serious artist - one of the most important of our time - has never been more solid.
Domingo has always been a risk taker. Though born to sing the beefy Verdi and Puccini roles he is identified with, he has been all over the vocal map - from bel canto to French opera. In recent years, he has been wading into Wagner's heldentenor repertory, despite warnings from opera-phile lifeguards that those Wagnerian waters are treacherous. The heldentenor roles call for a different kind of singer, someone with stentorian thrust and darker natural vocal colorings.
Yet through careful work and sheer determination, Domingo has been making these roles his own. Last year for the gala opening night at the Metropolitan Opera in New York, Domingo sang the demanding role of Siegmund in Act I of Wagner's ``Die Walkure.'' I listened, trying to think of a tenor in the world right now who could sing this role better. I couldn't come up with one name. This spring he brings his acclaimed ``Parsifal'' back to the Met. And he has accepted an engagement in Europe for 1996 to sing his first Tristan, a ``voice-killer'' even for the at best two or three tenors of every generation who can sing it.
Given Domingo's exploration of the weightier Wagnerian repertory, it is remarkable that he is at the same time taking on roles from still another realm of opera, the lighter vocal terrain of Mozart.
This season at the Met, Domingo is singing the title role in Mozart's ``Idomeneo,'' his first Mozart role at the house. Naturally, Domingo lacks some of the vocal agility and lyrical lightness that an ideal Mozart tenor should have. But Idomeneo is the one truly heroic tenor role in the Mozart canon. And it was thrilling to hear it sung by a true heroic tenor.
In the opera, King Idomeneo of Crete, returning finally triumphant from the war against the Trojans, is threatened at sea by a terrible storm. The battle-weary king makes a pact with Neptune, offering to sacrifice the first person he sees onshore if the god will return him safely home. But when he lands, the first person Idomeneo sees is his son, Idamante.
Stylistically, the opera comes from the ``serious'' (opera seria) tradition. But Mozart was not about to stick to the status quo. He melds arias, ensembles, and entire scenes into long musical-dramatic arcs. The opera centers on the king's attempt to pry himself from his promise. And the center of this performance was Domingo's Idomeneo.
DOMINGO shaped the long Mozartean lines with supple lyricism; every phrase had character and color. He did not exactly scale back his enormous voice, though he did shade and cover it in effective ways. The sound was plaintive and resonant. And when he did unleash his full voice in climactic moments, it was utterly gripping. This was no ruffled-cuff Mozart singing.
On stage with Domingo were two singers ideally suited to Mozart: the vibrant mezzo-soprano Susanne Mentzer as Idamante, the sublime lyrical soprano Dawn Upshaw as the Trojan captive Ilia. But the distinctiveness of Domingo's sound just made him seem more a king, isolated with responsibility, nearly broken by remorse.
On Domingo's off nights in April, in between his three performances of ``Parsifal'' at the Met, he will not be sitting around with nothing to do. He will conduct five Met performances of Puccini's ``Madama Butterfly.''