SAN FRANCISCO — The priest will be ordained in a purple Lutheran church. The Communion bread, symbolizing the body of Christ, will be gluten-free. The congregation will pray to "our mother our father in heaven."

But the real departure from Roman Catholic tradition will be evident when Maria Eitz approaches the altar Sunday for the laying on of hands that turns parishioner into priest.

Over the last decade, as the Vatican has faced a serious shortage of priests, a small but growing number of women have answered what they believe to be a call from God. California is home to more ordained Catholic women than any other state. Eitz — a retired theologian with four adopted children — will be the first woman ordained as a Catholic priest in San Francisco.

PHOTOS: Turning a parishioner into a priest

The more than 120 women worldwide who have been ordained as Roman Catholic priests and deacons say their faith gives them comfort and hope. But that same faith also is bound by Canon Law 1024. Short and blunt, the church edict states that "a baptized male alone receives sacred ordination validly."

The Vatican has said that women who presume to be priests, and those who help them, are committing a grave sin. And like Catholics who have abortions or commit heresy, female officiants are subject to the ultimate penalty — automatic excommunication. The church does not acknowledge ordained women or the sacraments they offer.

The first female priests were ordained in 2002 on a boat on the Danube by a bishop who previously had broken ranks with the Vatican. A year later, bishops who asked to remain anonymous until after their death for fear of reprisal ordained the first female bishops so that they, in turn, could ordain other women.

According to Roman Catholic Womenpriests-USA Inc., more women are expected to be ordained as priests and deacons in 2013 than in any previous year.

To Eitz, the threat of excommunication is meaningless. It has happened to her once already, when she became a deacon in 2012. She ignored it then and ignores it now, she said, because "if you are baptized, you cannot be unbaptized. If you are called to the table that God calls people to, you cannot be excluded."

The soft-spoken 72-year-old said she was taking the controversial step because "it is right and just."

"It needs to happen. Not so much for myself … but for the people who will come after," she said. "For the girls. For the other women."

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At 9:30 a.m. on the Saturday before Mother's Day, Eitz and Victoria Rue prepared for Mass at Sophia in Trinity, which describes itself as "a Roman Catholic community celebrating a radically inclusive God."

The adherents gather in a small chapel at the rear of Trinity Episcopal Church — whose main sanctuary was shuttered four years ago because the congregation could not afford to retrofit the 120-year-old sandstone fortress, with its Tiffany stained-glass windows and E.M. Skinner organ.

Like Sophia, most of the communities led by female priests meet twice each month, either in private homes or non-Catholic churches whose members sympathize with the effort to ordain women.

Eitz is Sophia's deacon; Rue is its priest.

Their first duties on this chilly spring day, however, were far from priest-like: They cleaned up a clutter of coffee cups and sugar packets and rearranged the chairs from straight rows into a circle. In its center, they set up the altar — a wobbly table steadied by a wad of paper napkins.

As two dozen or so worshipers filed into the chapel, Eitz and Rue donned crisp white clerical robes.

But not for long.

"As you know," Rue told the congregation, "Maria and I wear these robes because they are symbols of our baptism. But because … separation between the clerics and lay people is rampant in our Roman Catholic Church, Maria and I think it is very important to not wear them, these albs.