The first time Mary Jane Johnson sang in an opera, she was seen by 22 million people. That was in Philadelphia two years ago, when she starred with Luciano Pavarotti in an Emmy-winning televised production of "La Bohe me."

Johnson won that opportunity in a contest against hundreds of other singers from 33 countries: the first Luciano Pavarotti International Voice Competition. Her victory and her spectacular opera debut have launched her on a career that still seems improbable for a 34-year-old West Texas voice teacher who expected to spend her life giving lessons and raising her children.

She still seems astonished at it: "Do you realize that was the first thing I ever did? The very first staged thing!"

To top it off, her stage career began at the last possible moment. In 1980, she decided to take the plunge and enter the Metropolitan Opera regional auditions in El Paso.

"I did it at that time only because it was then or never," she said. "It was the last year I could enter it, agewise the limit was then 30 . It just happened like that. I never thought I would become a singer. I did the auditions just to find out if I could go on.

"I won in Texas, and then went on to New York but did not get in the finals."

While Johnson didn't win, it gave her the impetus to break out. Within three years she had trained in New York with the best teachers, including Loretta di Lelio, wife of celebrated tenor Franco Corelli; won the Pavarotti competition; became an annual star at the Santa Fe Opera; and signed on as an annual performer with the San Francisco Opera.

This month she is in the title role in Leha'r's "The Merry Widow" with the Washington Opera, a splendid performance that she repeats for the last time Sunday.

Starting from scratch and reaching Johnson's current level in four years is not the rate at which most successful opera careers develop, nor is 30 the conventional age to begin. That's almost like trying to turn tennis pro at the same age -- there's just too much catching up to do.

Her belated career, in some ways, reflects the changing concepts of how women balance professional and family priorities, especially in solidly Middle American West Texas.

"You see, my husband and I went to Texas Tech" in Lubbock, said Johnson, who is originally from Pampa, over a lunch of trout. "And we married when we were still in school, in '71. He was a basketball player, from Austin. And then we both graduated in 1972. We moved to Amarillo, and I started a voice studio. Then we moved to Abilene. He worked for Phillips Petroleum Company as a salesman. And I taught voice there at McMurry College. Then we moved back to Amarillo and I got my master's from West Texas State in Canyon, and taught at Amarillo College. "

They have a daughter, who is 6, and a son, nearly 5 months.

Through gradual studies, Johnson moved from mezzo to soprano -- "working and stretching the cords."

"I worked very hard at what I did," Johnson recalled, "directing opera workshops, conducting, preparing for productions. . ."

"I knew I had the talent," she said. "But at first, I had just gotten married and the most important thing at that time was getting a very strong relationship with my husband. I didn't think about it like that. It just happened like that.

"I just lived a day at a time, one of those situations where . . . I could never have done it then . . . sometimes it's just not the time.

"But I kept going to opera. I went to Santa Fe a lot. And remember thinking to myself . . . I would hear all these people sing, and they would be my age or younger. I can do this, and I can do as well, I said. My gosh, I've got this. And why should I just keep sitting in the opera and being frustrated in my chair for the next 20 or 50 years? I'm just not going to do that."

After the Met auditions, it was Johnson's husband, who was starting his own business, who finally decided that Johnson had to pursue a professional singing career: " 'I'm going to start pushing you,' " he told her.

She went to New York, taking her daughter, subletting an apartment and seeing her husband only when he came once a month for a long weekend.

"The first year all I did was study," said Johnson. "Loretta Corelli got me lined up vocally -- got it all right from top to bottom, and so forth. And there are very few who really know how to do it. I went through that very intensive work three times a week for an hour. And it was the best thing I ever did. And when I was able to get away from that I was working languages."

When news about the first Pavarotti competition began to spread, Johnson was sought out by the pianist and vocal coach John Wustman, who offered to be her sponsor.

Her first encounter with Pavarotti came one day as she was entering the Met after a diction lesson, "and Luciano was coming out the stage door and we just bumped smack into each other. And this was when he was really looking for young singers for his vocal competition. We were introduced and he looked at me and said, 'Are you a singer?' "

Of Pavarotti, Johnson believes: "I owe him a lot.

"I was looking for a way to get started. It's odd. They'll listen to you audition, but they won't hire you until someone else has hired you. They're not going to take the first step. And you see that's what Luciano did. He took the first step. He was not afraid. What did he have to lose?"

A week after the debut in "Bohe me" with Pavarotti, Johnson sang Adina in Donizetti's "L'Elisir d'amore" with the same company, the Opera Company of Philadelphia.

Next, she "found out there was a Rosalinda in 'Fledermaus' at Santa Fe. I got over there to John Crosby the company's head , and I got my manager to send along some information, and Mr. Crosby saw on the sheet that I had won the Pavarotti competition, and he like hired me on the spot."

Soon after, the San Francisco Opera's Terry McEwen "got on the bandwagon and hired me immediately. He got an audition in Carnegie Hall, which is the best place to sing for an audition. It's big and I can use all my voice . . . The next week he hired me to do Jenifer in Tippett's 'Midsummer Marriage,' and Freia and Musetta.

"And this year I went out and covered Montserrat [Caballe'] in 'Ernani' and got to do the final performance. It was a very good thing for me. It was my first Verdi. And I loved it, and it was with [Paul] Plishka and [Sherrill] Milnes. I mean, how can you do better. . ."

But there is the future. She has met with the Metropolitan Opera's artistic director, James Levine, "but I haven't heard anything from them." And there is the possibility of singing in Europe. "I've never even been there. And I don't want to do it until I'm comfortable," Johnson said. "But I do have a manager in London who has never heard me sing. And a manager in France I have never met in person."