Their numbers and influence may be declining, but American nuns demonstrated Wednesday what generations of schoolchildren already knew: They are a force to be reckoned with.

By sending a letter to Congress in support of the Senate healthcare bill, a wide coalition of nuns took sides against not only the Republican minority but against their own church hierarchy, as represented by the U.S. Conference of Catholic Bishops, which opposes the bill. The nuns’ letter contributed to the momentum in favor of the legislation, despite opposition that is partially rooted in a disagreement over abortion funding.

“We agree that there shouldn’t be any federal funding of abortion,” said Sister Simone Campbell, the executive director of Network, a national Catholic social justice advocacy organization that spearheaded the effort. “From our reading of the bill, there isn’t any federal funding of abortion.”

Moreover, she said, the reverence for life that underpins Catholic opposition to abortion also argues for passage of healthcare reform.

“For us, first of all, tens of thousands of people are dying each year because they don’t have access to healthcare, so that is a life issue,” said Campbell, who is affiliated with an Encino-based order, the Sisters of Social Service.

She said Network, which has long supported healthcare reform, drafted the letter within hours of hearing that the Catholic Health Assn., which represents about 600 hospitals, had come out in favor of the bill last week. The letter was signed by the leaders of more than 50 Catholic women’s orders and organizations, including the Leadership Conference of Women Religious, which says it represents more than 90% of the 59,000 American Catholic nuns.

The Catholic bishops issued a statement Monday opposing the legislation, while stressing their support for healthcare reform in general.

The bishops’ statement, signed by Cardinal Francis George of Chicago, said the bill, as currently written, was flawed because it would subsidize the purchase of health insurance plans that cover abortion.

George said the bishops disagreed with a Catholic Health Assn. argument that the bill was acceptable so long as it was “corrected” in follow-up legislation. He said that was “a little like asking us . . . to buy a pig in a poke.”

Catherine Mooney, a professor of church history at Boston College who has written widely about Catholic women’s orders, said it wasn’t surprising that the nuns would take a different position from the bishops.

“I think they’ve shown over the years that they’re not afraid to take a stand,” she said. “They’re speaking out for something that they think is a point of justice, and speaks for Gospel values.”

Clyde Wilcox, a professor of government at Georgetown University who studies religion and politics, said the nuns’ letter reflected a debate among American Catholics “between those who urge no cooperation with any government programs that support same-sex couples or abortion in any way . . . and others who favor policies that enhance social justice and provide benefits to the poor, even if this may mean some compromise on these issues.”

Campbell said the nuns’ disagreement with the bishops was one of interpretation, not substance.

“We agree on the moral principles,” she said. “It’s just whether the politics of this meet our moral principles. So we’re not having a fight -- I hope.”

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latimes.com