Opera composers are so set on pitting the tenor against the baritone in their plots that during tonight's "In Concert at the Met" telecast, Placido Domingo and Sherrill Milnes are able really to be friends only once--in the comradely duet of Rodolfo and Marcello from the last act of "La Bohe me."

But, fortunately, from the seeds of enmity springs some of the most rapturous lyricism in opera, as we hear in segments from "Otello," "La Gioconda" and "La Forza del Destino" on tonight's concert, which airs on Channel 26 at 8 and will be simulcast on WETA-FM (90.9). It was recorded on the Met stage Jan. 30. There are subtitles.

Both the tenor and the baritone are in grand form from beginning to end, with Domingo's voice, especially, just about as true and free as you could imagine in the first half. In the opening duet from Bizet's "The Pearl Fishers" and in the aria "Un di all'azzurro spazio" from Giordano's "Andrea Chenier," Domingo's range of vocal color and effortless power are quite remarkable. As the concert continues and Domingo tires, the voice tightens, but just a bit. And the encore duet, the scene in "Otello" in which Iago tells Otello about Desdemona's handkerchief, both men seem to get second winds, singing with shattering force, just as James Levine and the Metropolitan Opera orchestra produce a torrent of sound. No other two singers today handle this scene so grandly.

The entire second half of the program has Verdi pitting tenor against baritone. There are five excerpts from "Forza," in which the baritone, Don Carlo, is pursuing the tenor, Don Alvaro, to avenge the murder of his father, the Marquis of Calatrava. It is an opera that Domingo and Milnes have sung together many times.

Domingo opens with Alvaro's third-act aria, "O, tu chein seno agli angeli"; then there is the first of the duets, the one in which they pledge eternal friendship, and then comes the great baritone aria "Urna fatale," in which Milnes has his finest solo moment. Listen for his coloring of the middle voice and his soft high note just before the cabaletta; they are gorgeous.

Levine conducts a flaming performance of the "Forza" overture, magnificently played. And, finally, the singers do the final duet, "Invano Alvaro."

Early on, Milnes sings a rarity, the drinking song from Thomas' "Hamlet," which he revived this season at the New York City Opera. He brings such panache and force to this mediocre music that it sounds better than it is. The Enzo/Barnaba duet from "La Gioconda" seems the last word in operatic enmity, and the "Bohe me" is lovely.

Speaking of "Bohe me," Domingo drops a bit of a bomb in the intermission interview by announcing that he will make his Met debut as a conductor in "Bohe me" next season. Presumably he will not sing Rodolfo simultaneously.