Two years ago, researchers John and Sylvia Ronsvalle of Urbana, Ill., used a Lilly Endowment grant to examine American Protestant churches from an unusual perspective. What they found was not encouraging.

In a 164-page report, the Ronsvalles evaluated 31 denominations comprising 30 million Protestants in terms of members' putting their money where their allegiances were.Factoring out declines in membership and increases in inflation, converting all figures into 1982 dollars and dealing strictly with per-member giving and disposable personal income after taxes and inflation, the researchers concluded:

While Americans' spending power increased 31 percent from 1968 to 1985, the percentage of disposable income they gave decreased 8.5 percent. In other words, they found that people valued their "lifestyles" more than their church.

Sylvia Ronsvalle felt that if those trends weren't changed, churches would have less and less to spend on helping others after they met their upkeep bills.

The Ronsvalles found statistics for 26 of the 31 denominations, including all of the large ones such as Episcopalians, Methodists and Southern Baptists and 99 percent of the membership in the 1968-85 study. And, they recently told the North American Conference on Christian Philanthropy, they found things have not improved. Things have gotten worse.

From 1985 through 1988, the latest figures available, they said, Americans' disposable income after taxes and inflation increased by 8 percent, while the percentage of income given to those churches studied decreased by 5.64 percent.

Though the Ronsvalles acknowledge that their surveyed churchgoers' donations keep increasing in dollars - $302 a member in 1988 as compared with $296 a member in 1985 and $247 a member in 1968 - they argue that the churches are getting less and less priority for their members' money.