Churches are gaining in numbers while providing a vital source of charitable funds and volunteer activities, according to a study that says religious congregations devote nearly half the money they receive to charitable use.

The study, "From Belief to Commitment," says churches surpass foundations and corporations as financial resources for charities.The study was done by Independent Sector, a Washington-based group representing organizations involved in philanthropy and voluntary activities. The Gallup Organization assisted in the study released Wednesday.

The survey yielded much information on churches and their memberships in addition to the data on charitable activities.

For example, 54 percent of congregations reported that their memberships had increased over five years, compared with 18 percent reporting a decrease. Thirty percent of congregations were founded before 1900, 16 percent between 1900 and 1930, 25 percent between 1931 and 1970, and 15 percent since 1971, "indicating the continued vitality of religious institutions in the United States."

But the main aim of the study was to determine whether and how much church-related giving could be counted as evidence of the non-profit sector's service to society.

The study found that $19.1 billion of the $41.4 billion contributed in 1986 to congregations "was used in ways that express religious conviction about service to others."

In addition, volunteer activities by clergy and church members were valued in the study at $13.1 billion. Some 253,000 volunteer clergy gave an average of 70 hours per month, and 10.4 million volunteers other than clergy worked an average of 10 hours per month on congregational programs.

The survey found that nearly nine out of 10 of the nation's 296,000 congregations had one or more programs in human services and welfare, with a heavy focus on family counseling activities.

Seventy percent were involved in overseas charitable activities, and 56 percent were involved in institutional care such as hospitals, nursing homes or hospices.

"This study makes clear how very large their community services are, dwarfing all funds contributed to and by other voluntary organizations for local human services," says a foreword to the study. "The report documents that religious congregations are the primary voluntary service providers for neighborhoods."

The $19.1 billion given by congregations, mostly in the form of collections and pledges, was in addition to the approximately $11 billion contributed by other sources to religiously affiliated organizations such as schools, nursing homes and day care centers, the group said.

Of the $48.1 billion in total expenditures by congregations in 1986, $8.4 billion was donated directly to other organizations and individuals, the study said. Of that, $5.5 billion went to denominational organizations and charities, such as Catholic Charities; $1.9 billion went to other charitable organizations in the community; and $1 billion was given directly to individuals.

More than 100 denominations - Protestant, Roman Catholic, Mormon, Jewish, Muslim and others - and all regions were represented in the sample.