NEW YORK, March 13 (RNS) -- Candles and incense are on the wane in America's religious congregations, while the electric guitar and drums are gaining popularity -- and causing more dissension -- in the country's houses of worship, a new study shows.

The sweeping study of 41 religious denominations by Hartford Seminary found that churches and synagogues that embrace contemporary worship styles are also the most likely to increase their membership roles, but the transition is usually not without a struggle.

"Congregations that seek to change their style of worship have to pay the price of conflict," said Hartford researcher David Roozen, one of the principle authors of the "Faith Communities Today" study, released Tuesday.

The five-year project presents one of the most comprehensive looks inside America's houses of worship to date. The study found a more diverse religious makeup with once-nontraditional religious groups such as the Mormons and Muslims outpacing the growth of Catholics, Eastern Orthodox and Protestants.

Organizers say the project represents 90 percent of all churches, synagogues and mosques in the country, and is the closest thing to a religious census in the United States today. The study is sweeping in its depth, including everyone from Baha'is to Baptists, evangelicals to Episcopalians.

Among the report's major findings:

Half of religious congregations have fewer than 100 "regular participating adults," and 88 percent have fewer than 350.

Just over half of all congregations -- 52 percent -- are located in rural areas, while only a quarter are located in urban areas.

Congregational growth has been strongest in the American West, outpacing growth in the South and far surpassing declines in the Northeast and Midwest.

The future of American religious life is relatively rosy, according to the numbers, with half of congregations reporting some level of growth, while a third have leveled off and only 19 percent have lost members. The survey did not look for a total number of Americans involved in religious life.

Two-thirds of growing congregations can be found where much of the general population is now living -- in America's suburbs. Churches and synagogues say the fastest-growing congregations are the ones that place the strictest demands on members' time and lifestyles.

"Despite the challenges of changing community populations and the natural process of institutional aging, the vast number of congregations feel that they have been able to renew their strength and to sustain themselves," said researcher Carl Dudley.

Still, there are some troubling undercurrents for congregations looking to the future and trying to attract younger, unreached people -- most often by modifying their worship styles. Often the biggest strains on a congregation come when a less traditional, more informal worship style is adopted and older members feel at odds with their younger counterparts.

The study found that the largest congregations are the most willing to change, and older churches face more resistance. Only 37 percent of established churches -- those started before World War II -- welcomed wholesale changes, while two-thirds of younger churches embraced them.

Half of all megachurches -- those with 1,000 or more regular participants -- have changed their worship style, and researchers looked to instruments as one measure. Only between 10 percent and 15 percent of older churches use keyboards or drums, compared with about 30 percent of younger congregations.

The mainstay for most worship -- the piano or organ -- falls from 89 percent of older congregations to only 59 percent of churches started in the past decade. Nearly six in 10 congregations who reported conflict said they had also changed their worship "a great deal" in the past five years.

Roozen said the change in worship style follows a seismic shift in many Christian churches' approach to God. In the past, God has been viewed as an angry, judgmental diety. In recent decades, more emphasis has been put on the pesonhood of Jesus, resulting in a more personal and intimate view of God. Less structured, informal music better fits that changed view of God, he said.

"The bottom fell out for many of the mainline churches in the 1960s because the worship style didn't work" for the baby boom generation that was coming of age, Roozen said. Churches seeking to lure boomers back into the fold have found they also need to drop the liturgy they had always been using.

The Rev. Richard Houseal, research director for the Church of the Nazarene, said the findings present tough choices for churches whose members are aging but still want to attract new worshippers. The bottom line, he said, is that "those churches that changed their worship style ... were more likely to have grown."

The numbers also present challenges for religious leaders who struggle between the stable rural parishes that form the backbone of many denominations and the unreached urban centers. Often smaller rural congregations have a harder time recruiting clergy and paying the bills.

Monte Sahlin, a researcher with the Seventh-day Adventist Church, said three-quarters of his denomination is located in small towns or rural areas. The study shows "that we are not touching the urban mainstream of American culture."