Interfaith worship services have doubled in the decade since the 9/11 attacks, according to a new study released Sept. 7, even as more than seven in 10 U.S. congregations do not associate with other faiths.

The survey by an interfaith group of researchers found that about 14 percent of U.S. congregations surveyed in 2010 engaged in a joint religious celebration with another faith tradition, up from 6.8 percent in 2000.

Interfaith community service grew nearly threefold, with 20.4 percent of congregations reporting participation in 2010, up from 7.7 percent in 2000, according to the Cooperative Congregations Studies Partnership. After the attacks, “Islam and Islamics’ presence in the United States (became) visible in a way that you couldn’t ignore,” said David A. Roozen, one of the report’s authors and the director of the Hartford Institute for Religion Research at Hartford Seminary in Connecticut.

National Muslim groups tried to build bridges to other faiths, who in turn “reached out in new ways to be neighborly,” he said. Reform Jewish congregations led the way, with two-thirds participating in interfaith worship and three-quarters involved in interfaith community service.

The largest percentage of interfaith-worshipping congregations (20.6 percent) was in the Northeast, which is home to a disproportionate percentage of more liberal mainline Protestant churches. About 17 percent of interfaith-worshipping congregations are in a big city or older suburb, where greater diversity makes interfaith activity more likely.

The study implies that the more liberal a congregation, the greater likelihood for interfaith activity. Approximately half of Unitarian Universalist congregations held interfaith worship services, and three in four participated in interfaith community service. By contrast, among more conservative Southern Baptist churches, only 10 percent participated in interfaith community service, and five percent in interfaith worship.

The study shows most of the 11,077 congregations surveyed reported no interfaith activity, a finding that troubled the Rev. C. Welton Gaddy, president of Washington-based Interfaith Alliance.

“The reality in our nation now is we have a major problem with Islamophobia, and that fear is being fed by people in large enough numbers that we need probably ten times as many people involved in interfaith discussions and actions,” Gaddy said.

Even so, the fact that interfaith services and community projects have grown so much is something to celebrate, said Rabbi Marc Schneier, founder and president of the New York-based Foundation for Ethnic Understanding. “I’m not saying we are where we’d like to be, but the good news is the process has begun,” Schneier said. “Outreach to the Muslim community from a Jewish perspective is now becoming en vogue ... Ten years ago, if I would have proposed anything like that, people would have thought I was from Mars.”