THE FRESH-faced young woman breezes through the authorized-personnel-only door at the Kennedy Center's Terrace Theater and stakes out a place by an opera singer's dressing room. Inside, the singer is stripping off a bulbous phony nose, gobs of makeup and the raiments of an 18th-centruy Spanish nobleman. He has just spent the past three hours raging, brooding, raging, scheming and raging again as Bartolo in the Washington Opera's production of the "Barber of Seville" and now is turning himself back into a handsome, clean-cut young man in a modish leather coat. The woman, who has spent the past three hours in the audience concentrating on his phrasing and movement, jokes with others waiting in the stark, hospital-like backstage hall. "He's almost ready," she says, one ear trained on the door. "There goes his hair dryer."

The young woman is no ordinary Stage Door Jane. She is Gianna Rolandi, an up-and-coming coloratura whose talents have recently earned her roles that Beverly Sills used to sing. The young man, bass-baritone Joseph McKee, is her offstage leading man. Together, they are riding the crest of an opera wave that takes them from their base on New York's West Side to such places as Tulsa, Chicago, Calgary, London, Seattle and Los Angeles. They slip into their characters' identities somewhat as they slip into a new city, with the wait outside the dressing-room door one of the oft-played scenes. In a scenario suggesting the happier moments of Two For the Road, they are carving out their artistic careers, and, at the same time, a romance. t

Rolandi, a striking brunette of 28 with a smile as big as the Ritz, a soft, magnolia accent and an infectious laugh, is a soloist with the New York City Opera. When Sills decided to retire from singing and become the City Opera's new general director, Rolandi found herself cast as Cleopatra in "Julius Caesar" -- the role that vaulted Sills to stardom in 1966. On Monday night, she san Adele in "Die Fledermaus" in the televised farewell salute to Sills, her mentor. McKee, 33 and easy-going with a wry sense of humor, has been on the road more, experimenting with a variety of roles and forums. He just wrapped up his month's engagement with the Washington Opera as the raging old Bartolo.

Rolandi and McKee (to their families and friends, they are Carol -- an Americanization of Carolina, her first name -- and Joe) as part of a generation of young American opera singers who have rejected the European route to artistic success.

"unless you're a big star, they (the European opera companies) really put you in a straitjacket," he says. "You sign a contract over there for two years and do the same thing over and over," she adds.

For Rolandi, the choice came easily. The daughter of an American opera-singing mother and an Italian gynecologist, Rolandi "grew up around voice teachers, so it never occurred to me to do anything else." Her childhood home was Spartanburg, S.C., and she sang in her first opera at age 7, in the children's chorus of a Charlotte production of "La Boheme." As a student at the Curtis Institute in Philadelphia, she says she "pestered" a coach at the New York City Opera for an audition, getting the nod on the first try.

McKee, too, grew up wanting to sing -- "but I wanted to be a pop singer -- I wanted to be Bobby Rydell." His conversion came in the 7th grade, when he was taken to a student performance of "Don Giovanni" at the Met. He studied at Oberlin College's Conservatory of Music, and after a stint in the Army Chorus auditioned for Matthew Epstein of Colombia Arists Management. That 1974 audition landed him the title role in the "Marriage of Figaro" in Tucson.

A string of roles and cities later, the couple met at a New Year's Eve party a year ago at their manager's apartment. "A mutual friend introduced us and we just spent the rest of the evening talking together," Rolandi says.

A pair of opera singers, both pursuing the limelight, yet falling for each other. It invites comparison with the piano romance of "The Competition." Rolandi and McKee haven't seen the movie, but they have heard about it and say they are not Amy Irving and Richard Dreyfuss.

"We didn't get together on that basis," says McKee, noting that Rolandi had already been singing at City Opera and had just made her Met debut before that New Year's Eve party. "In the beginning," he says, "I wondered if it [competition] would be a problem. It was something I had to know about. Interestingly enough, I found out it hasn't been a problem."

She says she tries to think of her career as "a job -- if you took it seriously you'd be really neurotic."

Do they coach each other?

"Yes," says he; "no," says she.

He, clarifying, "She coaches me some; I don't coach her." He elaborates: "You have directors and conductors who don't have the personal interest in you or the ability" to fucus on one performer in an ensemble. Rolandi can draw on her experience in other productions of the same opera to make valuable suggestions.

"Carol is really into her career. She's making a transition," McKee says. "I'm still feeling my way. My voice won't get to maturity unitl I'm 35, or later."

If McKee faces any comparisons with Rolandi, Rolandi faces even more formidable ones -- with Sills. Rolandi has been singing many of Sills' best-known roles. Calling herself lucky that she "came along for the roles at the right time," Rolandi says, "I was ready to be compared to her. I had a couple of years to prepare for it. It's stupid to say I'll be another Beverly Sills. She's tremendous."

Rolandi says her new boss is also "such a nice lady." An example: "I was doing Daughter [Daughter of the Regiment, a popular Sills role] and she called me in and gave me some advice . . . . She gave me a different cadenza. She told me ways to keep an audience on the edge of their seats. There are ways of approaching notes. She said it looks so easy for me to sing high notes, that the audience doesn't believe that it's hard. The more exciting singers wait [a pause], it's more exciting for the audience to see if you're going to get that high note. She was right!"

"She's given me wonderful roles," Rolandi adds, describing Sills as "like a mother with all her children" proudly showing them that "she made it in this country -- you can be a success."

"A lot of times," Rolandi says, "whatever's going on in your private life lends itself to drama. I had done a bunch of Lucias in City Opera. In the fall my mother was sick, and it seemed that everything was going wrong." In Lucia's mad scene, "I was wearing my emotions on my arm. It was like a kind of therapy." The same critic who had reviewed her in the spring was back in the fall. His review, she says, began: "Nothing gives me greater pleasure than to talk about the growth of a singer . . ."

McKee, too, translates emotion into stage action, with comedic results. He recalls a tenor in Detroit who was "thrusting his hand in front of my face. I was livid. I envisioned breaking every bone in his body. I stuck my hand in front of his face, and got a very big laugh."

Rolandi has noticed her voice "taking on different colors" and with maturing come chances to attempt more demanding roles. She is branching out, doing Lucia and other Bellini works, Handel's "Caesar" and bel canto -- material with "more meat to it." But she takes care not to push her voice. Rolandi recently turned down $20,000 for a couple of weeks' work in Buenos Aries because she felt she wasn't ready for the roles: all four women in "Tales of Hoffman." "I talked about it with my manager. It wasn't right. But it was hard to say no."

McKee's favorite role: "Leporello in 'Don Giovanni.' He's not only funny, but he plays the regular gamut of emotions. That's the thing that makes him unique. He's kind of dry, his humor is dry, sarcastic. He follows Giovanni's life around, like he wants to be like him. He represents more the common man. He wants to be a stud and . . . he's stuck in his situation. But he has humor, he drops one-liners."

It's 1 p.m., and the weekday lunch crowd in the restaurant is beginning to thin out. But to Rolandi and McKee, whose normal workday often begins as the nine-to-fivers are heading home, it's morning. They look like a couple of college kids, each dressed in a tweedy blazer. Over eggs Benedict and coffee, they try to reconstruct their hectic itineraries, bantering, laughing, finishing each other's sentences. He was wrapping up his artist-in-residency in Cheyenne; she was rehearsing in New York. She joined him for a week in the Tetons, then flew back to New York to rehearse "Julius Caesar." "Joe stayed out there . . . no he didn't stay out there." He helps: "I went to Calgary to do Gilbert and Sullivan." When Carol had five days free, she joined him there. "He got back to New York on dress rehearsal day . . ." "I stayed there till Carol went to Toronto . . ."

Don't those schedules make it tough to keep a relationship going? "The airlines and phone company make a fortune off us," laughs McKee.

So far, they have no immediate plans to perform together -- she's booked into 1984 and he's booked through this year. But, they are thinking about shared billing in a for-keeps production: marriage. Can two opera singers, with demanding career schedules, make it work? "It depends on the people," she says. "Some [singers] can't do it -- their egos couldn't take it. They would feel jealousy."