Years ago, Laura Croen chose religion over opera. But she's never lacked for appreciative audiences. And tonight, she faces one of her biggest and most exacting.

As the Reform congregation at Temple Sinai in Northwest Washington begins celebrating Yom Kippur, or the Day of Atonement, Cantor Croen will stand before nearly 1,300 of her fellow Jews and sing the Kol Nidre prayer, petitioning God's forgiveness for promises unmet.

Robed in white, a kippah on her head, she will stand to the left of the temple's blue and silver ark and give her professionally trained voice to the ancient melody known as "MiSinai," or "From Sinai," which accompanies the prayer.

"Let all our vows and oaths, all the promises we make and the obligations we incur to You, O God, between this Yom Kippur and the next, be null and void should we, after honest effort, find ourselves unable to fulfill them," Croen will sing. "Then may we be absolved of them."

The services of Kol Nidre, or All My Vows, and those tomorrow on Yom Kippur are demanding not only for rabbis but also for cantors such as Croen. But singing is only half her job.

Typical of today's ordained, or "invested," cantors, Croen is also responsible for a vast array of pastoral and educational tasks. She visits the sick, prepares boys and girls for their bar and bat mitzvahs, helps plan the liturgy and officiates at funerals and weddings.

"We're not just the singers anymore," said Croen, 42. "We are also full clergy members."

Unlike in the past, when cantors generally acquired their skills through informal apprenticeships, a growing number are opting to attend cantorial school for a rigorous four years of religious education that includes studies of Jewish history, law and liturgy as well as music. And as Jews increasingly revert to traditional practices, the demand for cantors with such training has been greater than the cantorial schools can fill.

"Generations ago, all a cantor did was chant services. But when the cantorial schools were created almost 50 years ago, a decision was made that the cantor was going to be a full-time clergy person who would serve the community in myriad ways," said Henry Rosenblum, dean of the Harvey L. Miller Cantorial School and College of Jewish Music at the Conservative movement's Jewish Theological Seminary in New York.

Cantor Israel Goldstein, director of the School of Sacred Music at the Reform movement's New York seminary, Hebrew Union College-Jewish Institute of Religion, said the shortage of ordained cantors has arisen because "congregations are beginning to realize what a wonderful addition the cantor can make to the staff. . . . They bring a different dimension with their involvement in music."

In another trend, women are flocking to the two main cantorial schools. Three-quarters of Rosenblum's 32 students and two-thirds of Goldstein's 40 are women.

"A lot of women went through childbearing years and are in their forties and are saying, 'Now it's my turn' " for a career, Rosenblum said.

Kimberly Komrad, part-time cantor at the Conservative congregation of Beth Israel in Owings Mills, said she went to cantorial school to improve her job prospects. "To gain the respect and gain a position, I felt I had to have the credentials," said the 37-year-old graduate of the Conservative movement's music school.

Invested cantors, who can command salaries upwards of $90,000, sometimes get annoyed if those who have not gone through cantorial school are seen as their equals.

"A congregation could hire someone who just reads music and give them the title of cantor," said Michael Shockett, cantor at Falls Church's Reform Temple Rodef Shalom and a 1994 graduate of the School of Sacred Music. "But they don't have any seminary training. The real difference between a soloist who comes in on a Friday night and me is that we are clergy people."

The Orthodox movement of Judaism does not have a separate cantorial school, and its congregations are generally less likely to have cantors.

Croen, a native of Milwaukee, found herself in a dilemma similar to the one Al Jolson's character faces in the 1927 movie "The Jazz Singer": A young Jewish man must choose between a secular career as a cabaret singer or following his father's path as cantor at the family synagogue.

"I didn't know women could be cantors when I was a child growing up, though I loved Judaism," Croen said. But while pursuing a master's degree in vocal performance at the University of Rochester's Eastman School of Music, she auditioned for a part-time position as a cantorial soloist in a nearby synagogue. It was a personal revelation.

"I found my singing changed dramatically, and the experience was so fulfilling. . . . Something from my soul emanated in a very different way," Croen recalled.

"Even my voice teacher said my voice sounded completely different when I was singing Jewish music. I had a different connection than when I was singing German lieder."

Croen then "went through a lot of soul-searching. Up to that point, I was going to pursue a career in opera."

But as she discovered the pastoral aspects of a modern cantorship, she began to see it as a "richer experience." After obtaining her degree, she moved to New York and entered the School of Sacred Music, graduating in 1988. Five years ago, after serving as a cantor in San Francisco, she arrived at Temple Sinai.

Although some congregants would rather deal with a rabbi than a cantor in times of need, Croen said most do not blink if she turns up instead. "Sometimes someone will look a little surprised," she said, "but we make a joke in our congregation that it's not official that you're really sick unless the senior rabbi comes."

With a lot of weekend work, full-time cantorship is a demanding job, especially for women such as Croen, who has two children, ages 7 and 2. And though she now sings opera only "for fun," she has no regrets.

"It's a wonderful way to use your music," Croen said. "Helping people to pray, there is something unique about that experience."