NEW YORK (AP) _ Two exceptional leading women headed the cast of the Metropolitan Opera's first ''Il Trovatore'' since the 1989-90 season.

Soprano Aprile Millo was sick on Monday night and was replaced by Deborah Voigt, who was supposed to take over the role of Leonora later this season. Voigt has a voice in first bloom, with a lovely timbre for Verdi.

Dolora Zajick also was a youthful Azucena. She was passionate - Azucena can be positively hysterical - without making a rough or ugly sound.

Tenor Lando Bartolini was Manrico, the troubadour of the title. His sound is very pleasing. In the second half of the evening, he sounded tired twice but both times regained vocal freshness.

Vladimir Chernov sang Count di Luna with round, pleasing tones. Though the audience is on the side of the tenor, Chernov did sing tenderly. Jeffrey Wells also was good as Ferrando, the count's captain of the guard.

The chorus, which has a good deal to do in this opera, acquitted itself well. During the Anvil Chorus, one percussionist must have been seated among the singers. A ring on an ''anvil'' in the orchestra pit got an answering ring from him, right on the beat.

Nello Santi conducted with total consideration for the singers. Tempos were never rushed; beautiful singing was lingered over and relished by singers and audience. Bravos were heard often during the performance.

Visually, the stage has black steps its entire width, with a landing about a third of the way up. Often, a singer has an aria with nobody else on stage, so a flight of stairs is fine. But it makes the staging of trios quite static.

This ''Trovatore'' is more for sound than stage pictures. The stage is dark; there is some light on singers. Massive black pillars move in and out to create a cloister, a cell, etc. In this production, new in 1987, bonfires are used for chilling dramatic effect.