Verdi's "Don Carlo" is one of his great operas but it is also one of the most difficult to present convincingly unless you have six outstanding Verdi singers in the cast.

On Friday night at Wolf Trap not much happened until shortly after 10 o'clock although the curtain had gone up at 8. The problem centered around the fact that the powerful cast that sang in the Metropolitan's revival of the opera during the past season was not on hand. And this year for the first time, the Met is giving the complete opera much as Verdi wrote it for the Paris Opera.

In that version, Elizabeth and Don Carlo meet in the forest of Fontainebleau, believe they are to be married, and then find out that instead Elizabeth must marry Carlo's father, old King Philip II of Spain.

From there on, tragedy, compounded by the Spanish persecution of heretics at home and the Flemish in the Netherlands, gives Verdi scope for some great writing. His scorn for organized religion, personified by the Grand Inquisitor, never reached more open heights.

Unfortunately, neither Gilda Cruz-Romo's Elizabeth nor Vasile Moldoveanu's Carlo had the vocal resources to ignite the fires Verdi prepared. Thus restricted by his singers, James Levine could not do much in the pit until stronger artists appeared.

This did not happen until the Princess Eboli, Carlo, and his friend Rodrigo met in a garden and found themselves in a grand Verdian trio brought about through mistaken identities. Ryan Edwards, though his baritone is a bit light for Rodrigo, is a superb singer and artist. Nadine Denize, though she had just previously messed up Eboli's Veil Song, can sing very loudly. Something in her voice brought out a warmer response from Moldoveanu. None of it was great, but it was a start.

There followed the opera's largest scene, the burning stake of a bunch of heretics, of whom only two appeared. One of Verdi's exciting crowd scenes, it carried things to a somewhat higher level.

The truly great singing of the evening came from Jerome Hines as King Philip. With every bit of vocal authority and skill, he moved through the famous "Ella giammai m'amo" aria in a way that brought appropriate thundering cheers from the big audience.

That was followed by the tremendous dialogue with the Grand Inquisitor. James Morris, though lacking the huge black voice needed for the part, was immensely impressive, and with Hines, made the scene the finest of the evening. John Cheek was an excellent friar.

Denize had all kinds of trouble with her big scene "O don fatale," and Cruz-Romo did little with the aria in the last act. It was not a very good night, with the orchestra giving some sloppy intonation, not for the first time in the week. The chorus, in its varied assignments, was first-rate.