Believe it or not, politicians used to be able to assume that when the U.S. Catholic bishops spoke on an issue, that meant that the nation's Catholics had spoken. That was so mid-20th century.

Before long, Catholic liberals -- backed by Playboy's Hugh Hefner and others -- would dare to create a pro-abortion-rights group called Catholics for Free Choice.

Before long, American Catholics would become so divided that traditionalists felt the need to form a group called Priests for Life.

Catholics were not the only believers rocked by the earthquakes of the 1960s and '70s. Evangelicals ventured out into the public square, inspired first by a born-again Democrat from Georgia and then by the Hollywood Republican who promised to defeat him. The Protestant mainline declined and then splintered. Pluralism and globalization tested old coalitions and inspired old ones.

All of this caused radical changes in the nation's capital. The number of organizations engaged in advocacy work linked to religious issues has increased fivefold in four decades -- from 37 in 1970 to at least 211 today.

"No matter how small the group, everyone feels the need to open an office in Washington, D.C., so that their voices can be heard," said political scientist Allen D. Hertzke of the University of Oklahoma, lead researcher for a new study of religious advocacy groups conducted by the Pew Forum for Religion and Public Life. "All of this is evidence of the growing pluralism on the American scene and the fact that religion is playing an even more prominent role in our politics."

According to this survey, Catholics of one stripe or another are behind one out of five (19 percent) of advocacy groups with offices in Washington, D.C., and evangelical Protestants support almost as many (18 percent). While 12 percent of these groups are Jewish, only 8 percent represent the old Protestant mainline. In fact, Muslims support 17 advocacy groups, while the historic mainline churches now have 16.

Hertzke said it's significant that the largest category -- one quarter of the groups studied -- consists either of interfaith groups or organizations that work on religious issues that involve believers in multiple faith traditions. Nearly two-thirds of these groups work on both domestic and foreign issues.

While one church-state lawyer's "advocacy" is often another's "lobbying," 82 percent of the groups in the Pew Forum study operate as nonprofit, tax-exempt organizations. Thus, they focus most of their work on public policy issues broadly defined, as opposed to specific legislation or candidates.

However, the survey's broad definition of "religious advocacy" included "attempts to influence, or urge the public to influence, specific legislation, whether the legislation is before a legislative body, such as the U.S. Congress or any state legislature, or before the public as a referendum, ballot initiative, constitutional amendment or similar measure." It also included "efforts to affect public policy, such as activities aimed at the White House and federal agencies, litigation designed to advance policy goals, and education or mobilization of religious constituencies on particular issues."

It was easy to describe the groups doing this work in the years after World War II. They were "largely denominational," explained Hertzke, each representing a specific body of believers -- Catholics, Jews, Baptists or mainline Protestants, such as Episcopalians, Methodists, Presbyterians, Lutherans and others.

By the start of the 1970s, evangelicals were gaining power through the growth of nondenominational groups, educational institutions and media ministries. Then Roe v. Wade changed the shape of American politics -- especially for evangelicals and traditional Catholics. Meanwhile, President Jimmy Carter inspired some Baptists and infuriated others. The ground was moving.

Many of the advocacy groups launched during this period were ecumenical or interfaith, uniting liberal and conservative believers on opposite sides of hot-button social issues. At the same time, some historic churches began to splinter.

In the '90s, religious activism went global in a world transformed by the fall of Soviet Union, digital communications and growing Third World concerns about poverty, human rights, AIDS and religious liberty. Meanwhile, the face of religion in American began to grow more complex before and after 9/11.

"There has definitely been a globalization of religious advocacy work, with all of these trends and issues making their way back to Washington," said Hertzke. As a result, "ecumenical and interfaith work is now normal. We all live and work in the same world, now. Everything is connected."