If researchers want to uncover the roots of America’s bitter divisions on abortion, the first thing they should do is ask millions of citizens this question: How often do you attend worship services?

This has been a consistent pattern in recent surveys, and it can be seen in most pews, from conservative evangelicals to liberal mainline Protestants, said Greg Smith, senior researcher at the Pew Forum on Religion and Public Life. The pattern is especially clear among American Catholics.

“The people who attend worship services more often are going to be opposed to abortion, and those who rarely or never attend are going to support legalized abortion,” he said. “You go once a week? It’s going to be about two-thirds against. Rarely if ever? It’s about two-thirds in favor. ...

“That division is still there. But the big news is that both of these groups have been moving in the same direction for the past year or so.

We’re seeing support for abortion rights weakening across the board.”

A new Pew Forum survey found that the percentage of Americans saying they believe abortion should be “legal in all/most cases” fell from 54 percent to 47 percent during a single year. Meanwhile, the percentage who said they believe abortion should be “illegal in all/most cases” rose from 40 percent to 44 percent. The “undecided” camp grew from 6 percent to 9 percent of those polled.

“The nation remains pretty evenly divided,” Smith said. “However, what we can see is that support for legalized abortion is weakening in many groups, and it’s stalled in others. ... How much people practice their faith is a crucial factor in this.”

Support for abortion rights remains high among American Jews, but the latest Pew survey showed a drop from 86 percent in favor a year ago to 76 percent now. Support among Americans with no religious affiliation fell from 71 percent in favor of legalized abortion to 68 percent.

One of the most dramatic shifts came among members of white mainline Protestants — liberal churches that have consistently supported abortion rights. The numbers were especially dramatic when church attendance was factored into the equation.

Support for abortion rights among mainliners who attended church once a week fell from 54 percent to 42 percent, while support among those who said they attended less often fell from 68 percent to 60 percent.

To no one’s surprise, opposition to abortion rights among evangelical Protestants remains high, but the numbers have risen even higher in the past year. Church attendance is a major factor, with 79 percent of white evangelicals who worship once a week saying abortion should be “illegal in all/most cases.” A year ago, 73 percent took that stance.

Among white evangelicals who go to church less often, opposition to abortion rose a dramatic 12 percent — from 47 percent to 58 percent.

The contrast between regular and occasional worshippers was also clear among white Catholics. Opposition to abortion rights rose from 57 percent to 67 percent among Catholics who reported going to Mass once a week. Among those who said they attended Mass less often, support for legalized abortion declined slightly during the past year, from 65 percent to 62 percent.

These numbers are logical because Catholics who are active in the church are exposed more often to sermons, prayers and ministries that incarnate church teachings on the sanctity of human life, said Deirdre McQuade of the pro-life office at the U.S. Conference of Catholic Bishops.

“Those who are less invested in the sacraments — attending church, receiving the Eucharist and going to confession — may have less access to the truth about life, and fewer resources to believe and accept it,” she said.

In the end, stressed Smith, this survey underlines two realities.

First, there is little evidence that America’s debates about abortion are fading. Second, it’s clear that religious faith and practice remains one of the most crucial dividing lines on this issue.

“It’s important to realize that millions of Americans see themselves as caught in the middle” on abortion issues, he said. “Take those mainline Protestants, for example. Even though it seems that their support for legalized abortion is weakening, they probably see themselves as moving from one position in the middle to another position in the middle. They may be changing what they believe, but not very much.”

 Terry Mattingly is director of the Washington Journalism Center at the Council for Christian Colleges and Universities and leads the GetReligion.org project to study religion and the news.