Marilyn Horne on what makes a singer a diva:

"She is the one who will dig in her heels and say, 'This is the way it is going to be! . . . I've always said there are times when you have to risk everything. And you have to say to yourself that the worst that can happen is that you can lose. You have to be able to have the courage. Say you are in negotiation with La Scala, and you want such and such and such and such. And they say no. And they realize that this is an opera that you've been dying to sing and want to sing it at La Scala and that you hate to lose it because of certain things that you want. But you say you'll risk it all if you don't get the right conductor, the right producer, ip,2 the right money and all that."

That, says Horne, is what it takes often to produce the best ingredients for a production. "A lot of times everybody depends on us to open our mouths. I'm willing to take the heat if I get what I want."

Horne is a diva. She is 32 years into an operatic career of the greatest distinction. Not only is she the finest coloratura mezzo we have, but she's probably the grandest one within living memory.

Her impassioned declaration on the subject on divas came during a discussion with soprano Montserrat Caballe' after the two arrived here for a recent recital at Constitution Hall. Caballe', with an enormous voice topped by some of the most ravishing soft highs of recent decades, is every bit the diva as well, and the two gave visual demonstrations of the art with their arrival.

Trappings themselves do not a diva make, but they both had them in spades. They were getting here late on a cold day after flying in from wintry Missouri, where they had given a concert the night before.

First, into the small, chic hotel lobby rolled a huge baggage cart loaded with 12 bags, big ones, along with countless smaller ones. Then appeared Caballe', an ample lady of regal bearing almost totally enshrouded in fur, enough mink to carpet a room. Then followed Horne, newly svelte, in a trendy coat alternating strips of mink with strips of leather. It was like an entrance of two Elizabeth Taylors at the same time.

The singers' joint concert here, which went on for an unusual three hours, and the recent concert version of Donizetti's "Anna Bolena," starring Dame Joan Sutherland, are part of an escalating trend toward opera in concert form.

"I love concert opera," said Horne, "It's great because you have the immediacy of the audience right in front of you. You aren't behind the barricade of the orchestra. You don't have to worry about carrying around weighty costumes that you may end up catching on a nail. Montserrat and I have have done Rossini's 'Semiramide' over and over in concert. I don't think that the performances in the theater have been any more successful."

"In fact," interjected Caballe', "there is a special electricity about concert opera. Maybe it is because they can see us better. Maybe it is because the music is not disturbed by anything else . . . It is easier to concentrate on a phrase."

Everything is exposed in concert opera, noted Horne. It's that particular kind of excitement. "That's one reason why there are such great opera freaks in the world," she observes. "It's like walking a tightrope. It would be so thrilling to see somebody fall off. Not that they really want us to fall off. But it would be thrilling to be there when somebody falls off without a net . . . "It's definitely athletic," Horne continued. "We are definitely half athletes. Half artist, half athlete. Don't you agree, Montserrat?"

"Absolutely. At least 50 percent. Maybe more. It concerns how we all support our respiration. All our strengths."

The linkage between these two singers goes all the way back to their apprenticeship during the late '50s at small German provincial houses. Caballe' was at Bremen on the recommendation of conductor Josef Krips and Horne at Gelsenkirchen with the blessing of conductor Erich Leinsdorf.

"I was reminding Montserrat just today," recalled Horne. "We had a crazy Mexican-American singer from Brownsville, Texas, a guy named Alfredo Astarsa. He went from Gelsenkirchen to Bremen. And he came back to visit us, and he said, 'Jackie Horne's nickname , there's a girl up there who sounds just like you. She has the same kind of dark soprano, with the same kind of technique. And her name is Montserrat Caballe'.' That was 1958 or 1959. We're star-crossed lovers," she says, to gales of laughter from both.

They were supposed to sing together at one of the most historic occasions in opera of this era, the eight-hour gala on Oct. 22, 1982, observing the centennial of the Metropolitan Opera -- in one of the duets from "Semiramide" that they sang in the recent program here.

But Horne decided not to. "I sang 'Samson and Delilah' in San Francisco the night before and had to sing it again two days afterward. And I said I can't sing 'Semiramide' if I'm singing Delilah. They're worlds apart. So I said to myself, 'Honey, it's gonna be 'Mon coeur s'ouvre a ta voix' 'My Heart at thy sweet voice' for you' "

That choice produced perhaps the most dramatic moment of the entire gala, when, after she was finished, Horne walked to a group of retired singers at the side of the stage and embraced Rise Stevens, the most celebrated Delilah of the previous generation.

"I didn't know I was going to do it myself," recalls Horne. "Some jackasses wrote that it was calculated and everything. You know what really happened? First of all, I didn't know all those former great singers were sitting on stage until I got there. I walked out on stage and I saw them sitting there. And I was sort of halfway through the aria and I suddenly thought, 'Oh, my God. You're standing in front of Rise Stevens, singing her role and she owned this aria.' She literally owned it. Oh, she was so glorious in it. And I felt that I just had to acknowledge her. And that's all. I thought of doing it. And so I did it."

In that group also was the imperious Zinka Milanov, whom Horne remembered as "a great, great singer. But her character left a lot to be desired."

Once, remembers Horne, the haughty Milanov was singing Norma at the Met with Jennie Tourel as Adalgisa.

"Zinka was not a great Norma. She had the voice for it. But in those days they really slopped the coloratura out a lot. And Jennie got these great reviews but they just blasted Milanov.

"And do you remember in the old Met how you had to walk past the star dressing room to get to the others? Well, the next night Milanov got there first and waited behind the door of her dressing room until Jennie came in. Jennie arrived and as she walked past the door Milanov opened it and she said in her Balkan accent , "Heppy?" and then shut the door.

It reminded Caballe' of a story about Birgit Nilsson, who had one of the biggest voices in opera. "It was an 'Elektra' at the Met and rehearsals were going on. Leonie Rysanek, who was singing Chrysothemis, was sitting there on the stage at a table with someone else, when Nilsson came in vocalizing, 'Ya-Ya' and so on. Rysanek turned to the other person and said, "You see, to be able to sing in this house, you have to scream like her."

But both agree that Nilsson, who is now retired, had a grand sense of humor. Horne recalls a period when she was singing Bru nnhilde's Immolation Scene from "Go tterda mmerung" in concert, and Nilsson sent her a note saying: "If you don't stop singing Bru nnhilde, I'm going to start singing Arsace in 'Semiramide' ."

And Caballe' recalls with particular gratitude her first performance with Nilsson, at the Teatro Colon in Buenos Aires, as Liu to Nilsson's colossal Turandot in Puccini's "Turandot." "I was pregnant with my boy. And it was the second Liu in my career. And it was a very nasty conductor and he didn't like what I was doing. He thought I was using the wrong phrases or something. And at one point he was so nasty to me, and he didn't want to have me. And that day Birgit said to him, 'Listen, either she is my Liu, or I don't sing Turandot.' And we went on and it was a great success."

It is getting late and is time for the divas to watch their favorite television shows.

Horne is waiting for "The Colbys."

Caballe' is looking forward to "Dynasty," she says, and is disappointed to hear that it was on the night before.

Caballe' inquires, "Oh, and did you watch 'Sins'?"

Horne replies firmly, "Montserrat, I refused to watch 'Sins'."