(RNS) One year after a majority of Americans said they hoped the sour economy wouldn’t impact their church giving, three in 10 Americans now say they’re putting less in the offering plate, a Barna Group study shows.

Compared to a similar study that Barna conducted at the end of 2008, the percentage of Americans who have reduced their donations has increased by a staggering 45 percent.

Many of those who traditionally give to their congregations have been able to maintain their usual level of giving, but those who have not often substantially reduced their giving. Almost one-quarter of church donors cut their contributions by at least 20 percent.

“The implication is that church and nonprofit leaders should prepare for another lean year,” said David Kinnaman, president of the Barna Group.

The Barna study was based on telephone interviews in January and early February with a nationwide sample of 1,008 adults; it has a margin of error of plus or minus 3.2 percentage points.

The new findings signal a departure from previous indications about optimism in giving despite the gloomy economy.

A year ago, a separate survey of U.S. donors by Cygnus Applied Research found that more than half of actively religious donors planned to give the same or more to charitable causes in 2009 as the year before.

In addition, that survey also found that 43 percent of actively religious respondents remained “seriously committed” to giving in the face of economic uncertainty, compared to 23 percent of those who were not religious at all.