Soprano Catherine Malfitano spent the first five years of her career singing lyric soprano roles, getting good notices and wondering if her career was on the right course. Her "Monon" here several years ago won generous praise, but it wasn't cast in the kind of superlatives that would carry her quickly to the Met.

Meanwhile, some of her mentors were telling her that as fine as her voice was, she ought to relearn singing technical and also branch out into the strenuous coloratura roles associated with a Callas or a Sills. Conductor Colin Davis of London's Covent Garden told her that. So did George London of the Washington Opera.

"They kept telling me that I had a flair for this, that it was a shame not to dot it," she said this week.

Finally, about a year ago, Malfitano stopped stalling and followed their advice. She hired coach Dick Marzollo and started work on glittery parts like Lucia from "Lucia di Lammermoor" and Constanze from Mozart's "The Abduction From the Seraglio."

Another part was Alina - the simple country farmer with lots of difficult high notes - in Donizetti's "The Elixir or Love," a role she is singing with the Washington Opera this week.

Malfitano, hwo is a most comely 29, agrees that the experience of changing a vocal style well into a career is not unlike that of psychological analysis. "They not unrelated. You have to want to change before it does you any good, and that's what held me up so long. Your mind has ot be open, because, you know, if you want to sing well it has to come from the mind.

"Until then I sang best in English, and they said I should be doing better than that. I got well into my career before I understood how important it is to sing Italian vowels on. When you learn to sing Italian well, you sing other languages better."

This change has resulted in the brightening and evening of Malfitano's voice. It gives her singing a greater clarity and added thrust. "George London had been telling me I needed that for several years," she said. "The voice tended to be dark. I like anything that has dark passion, and I like dark colors. I guess I was afraid changing my voice would lead to a bland, monochromatic sound."

Malfitano thinks a major factor in the swiftness of her vocal transformation is her relationship with Stephen Holowig, the New York City Opera's assistant music administrator. They married two weeks ago. Holowig, 32, was once a singer, and, she says, "Because of him, getting married and the new singing are linked. It turns out I wanted to change my life in more than one way. And the result is a new openness in which one aspect feeds the other."

Holowig interjects that "it's difficult to get married in this business." Many people in opera never get around to it, and their personal lives, as a result, linger in indefinite instability. "You're in such close contact with the same large groip of people all the time that it's tempting just to go from one affair to another."

The course of a singer's career is determined by the phases that are formed by the development of the voice. As Malfitano observes, "Sometime after 35 my voice is going to change even more dramatically, but I don't have any way of knowing how."

Meanwhile she is moving into a colloratura phase intensively. Next fall she will make her first major recording, "The Abduction From the Seraglio," under Colin Davis. Next winter she takes on one of the most popular and taxing roles in her new range, Violette in Verdi's "La Traviata."

Thereafter, each successive role will press her a bit more. "Maybe I'll take crazy risks," she grants, "but I really don't know what my limit is, and I'll have to find out." "Norma?" she is asked. "Absolutely." "Tosca?" "Well, I don't think that's too farfetched."

Then, Holowig asks in jest, "Are you going to tell him about 'Don Giovanni?" she replies, "Oh. Don't you think that's going too far" So the reporter is forced to guess which role. He keeps naming women characters from the opera and getting no for an answer. Finally, the only one left is Donna Anna, one of Mozart't most exacting roles and one normally assocated with large voices.

She plans to continue her present close association with the New York City Opera, but unblushingly admits, "there are certin roles I'm purposely not doing at the City Opera so that some day I can do them at the Met" (her father plays violin in the Met orchestra). She shows every sign of confidence that day will come before long and points to the fact that Sills now performs in both houses.

Holowig is asked if he doesn't have mixed feelings about his wife moving across Lincoln Center from his company to another, and he says, "Not at all." He is asked why and a converstion ensures that finally gets to the subject of his own ambitions. He cuts in and says, with a laugh, "Look. The plain truth of the matter is that I wouldn't mind managing the Met myself some day."