A voice of astounding power. She will sing in opera broadcast Saturday. GHENA DIMITROVA

It is rare in this age to have an unsuspecting audience gasping in amazement at the sheer visceral impact of a huge voice. But this stir invariably occurs when an audience encounters Ghena Dimitrova's gleaming soprano for the first time. The rafter-rattling power of her voice in a confined space may not be appreciable on the national Metropolitan Opera radio broadcast this Saturday (1:30 p.m. in New York; check local listings), with Dimitrova singing the title role in Puccini's ``Turandot.'' But at her December Met debut in that role, the collective shiver continued long after the reverberation from the first climactic phrases of her opening aria had died away.

Something close to its unique presence can be sensed on the Bulgarian soprano's splendid new ``Tchaikovsky Arias'' recital album on CBS Masterworks (MK 42174, digital CD).

So it was a distinct pleasure for this writer to sit down and talk with Dimitrova a few months before that Met debut in a conversation that encompassed her training, her ca-reer, and her favorite roles. She had first come to my attention as a name in European opera reviews. Then a Bulgaraton aria recital record arrived on these shores, demonstrating that this was an ample, even huge, sound, capable of being reined in for some very effective quiet, or pianissimo, singing.

The first time I heard her live was at her New York debut as Abigaille in Verdi's ``Nabucco,'' with the Opera Orchestra of New York, in 1984. The evening set the local opera world abuzz for months, not just because she was actually able to sing all the notes of what is considered an unsingable role, but because Dimitrova possesses one of the largest instruments to be heard on any lyric stage today.

Dimitrova knew from an early age that she would be a singer. In conversation, she cites the proliferation of choirs in her country, where everyone is encouraged to sing. At school she was being told to push for a vocal career; at home, her father wanted her to study medicine. But the conservatory won out.

Her teacher, who trained in Italy and had earlier taught the remarkable bass Nicolai Ghiaurov, began her as a mezzo. It was soon clear that, though the bottom voice was naturally rich, the top was stretching easily into the soprano range. Added to that, in her words, ``I had a natural facility in [vocal] agility.

``At 18 I entered the conservatory; at 25 I left,'' she recounts, explaining that she went straight into the Sofia Opera, where her first role was Abigaille. There, she won the Sofia Competition, which was the first step on her way toward international stardom.

``I came out of Bulgaria when I was 29 or 30,'' she said. ``This is the time to begin a real career. After I won the prestigious Sofia Competition, I studied at La Scala. The first year there, I sang in eight Verdi operas.... The old singers took six to eight years of study. Today, they want a big career after two years.

``There are singers who start singing at 22 and at 27 have no more voice. This is because a 22-year-old singer who sings [Verdi's] `Traviata' cannot, at 24, sing `Turandot' and `Macbeth.' It is a terrible blunder.''

Building a career has not been easy for Dimitrova. A voice this large is never the most reliable of instruments, and she freely admits that, if she is not in perfect health and well rested, she cannot always deliver her best. She is immensely self-critical, but she has a clear sense of her worth as a singer and her place on the current vocal scene. Nevertheless, the Met was closed to her for nearly seven years, because the casting director at that time did not want her there.

Then, in the early '80s, the up-and-coming conductor/philosopher Giuseppe Sinopoli proclaimed her a force of nature, demanding her for a new production of ``Nabucco'' in Berlin and for his Deutsche Grammophon recording (2741 021, digital, three LPs). The production was a huge triumph for her, less so for him; the recording focused on the orchestra, and made her enormous voice sound distant, even faint. Then, as suddenly as Sinopoli proclaimed her, he denounced her. The recordings he has since made of the operas in her repertoire have been made without her participation, to the evident detriment of the performances.

``When I was younger, I suffered from these things, but no more. I sing with pleasure. I sing the greatest roles. No one sings `Nabucco,' Gioconda, Norma, Lady Macbeth, as I sing these roles.'' As with so many great artists, she can be objective about her talent, and happily, her reviews more than amply back her up. And to the above list of roles, I would add her grandiose, soaring Leonora in Verdi's ``Il Trovatore'' for the San Francisco Opera.

Dimitrova is fully aware that the art of singing is in serious decline around the world because of the pressures for instant careers. Her dream, at some point, is to establish a singing school, where she can re-instill the old-fashioned virtues of patience, thorough training, and a full understanding of the strengths and shortcomings of one's voice.

Meanwhile, the Dimitrova phenomenon continues with triumph after triumph, and the career moves on unabated.

For the home listener there are some fine samples of her art. There is the above-mentioned ``Nabucco'' as well as four recital albums, including her EMI/Angel debut recital (DS-38074), which I hailed as the finest example of the genre when it first came out but which, inexplicably, has not yet been transferred to CD. Videos of her ``Turandot'' and ``Nabucco'' from Verona capture her in peak form. I have not yet seen her performance as Amneris (in Verdi's ``A"ida'') from La Scala. Her Griselda (in Verdi's ``I Lombardi'') finds her in less than peak voice, but in blazing, defiant temperament throughout.

Dimitrova's calendar is solidly booked through at least 1991. Her main worry today is finding enough time to rest: ``I need the sun!'' she declares with a smile of anticipation.