On the 197th birthday of Charles Darwin, ministers at several hundred churches around the country preached yesterday against recent efforts to undermine the theory of evolution, asserting that the opposition many Christians say exists between science and faith is false.

At St. Dunstan's Episcopal Church, a small contemporary structure among the pricey homes of north Atlanta, the Rev. Patricia Templeton told the 85 worshipers gathered yesterday, "A faith that requires you to close your mind in order to believe is not much of a faith at all."

In the basement of an apartment building in Evanston, Ill., the Rev. Mitchell Brown said to the 21 people who came to services at the Evanston Mennonite Church that Darwin's theories in fact had compelled people to have faith rather than look for "special effects" to confirm the existence of God.

"He forced religion to grow up, to become, really, faith for the first time," Mr. Brown said. "The life of community, that is where we know God today."

The event, called Evolution Sunday, is an outgrowth of the Clergy Letter Project, started by academics and ministers in Wisconsin in early 2005 as a response to efforts, most notably in Dover, Pa., to discredit the teaching of evolutionary theory in public schools.

"There was a growing need to demonstrate that the loud, shrill voices of fundamentalists claiming that Christians had to choose between modern science and religion were presenting a false dichotomy," said Michael Zimmerman, dean of the College of Letters and Sciences at the University of Wisconsin Oshkosh and the major organizer of the letter project.

Mr. Zimmerman said more than 10,000 ministers had signed the letter, which states, in part, that the theory of evolution is "a foundational scientific truth." To reject it, the letter continues, "is to deliberately embrace scientific ignorance and transmit such ignorance to our children."

"We believe that among God's good gifts are human minds capable of critical thought and that the failure to fully employ this gift is a rejection of the will of our Creator," the letter says.

Most of the signatories to the project and those preaching on Sunday were from the mainline Protestant denominations. Their congregations have shrunk sharply over the last 30 years. At the same time, the number of evangelical and fundamentalist Christians has risen considerably, and many of them, because of their literalist view of the Bible, doubt evolutionary theory.

The Clergy Letter Project said that 441 congregations in 48 states and the District of Columbia were taking part in Evolution Sunday, but that was impossible to verify independently. Around Chicago, two churches that were listed on the project's Web site as participants in the event said they were in fact not planning to deliver sermons on the subject.

Still, those who did attend sermons welcomed what they heard. After the service at St. Dunstan's, Brett Lowe, a 41-year-old computer engineer, sat in a pew as his son Ian, 2, and daughter, Paige, 6, played at his side. "Sermons like this are exactly the reason we came to this church," Mr. Lowe said.

"Observation, hypothesis and testing — that's what science is," he said. "It's not religion. Evolution is a fact. It's not a theory. An example is antibiotics. If we don't use antibiotics appropriately, bacteria become resistant. That's evolution, and evolution is a fact. To not acknowledge that is to not acknowledge the world around you."

Jeanne Taylor, 65, a recently retired registered nurse attending services at St. Dunstan's, said the Bible was based on oral tradition and today "science is a part of our lives."

At the Evanston Mennonite Church, Susan Fisher Miller, 48, an editor and English professor, said, "I completely accept and affirm the view of God as creator, but I accommodate evolution within that."

To Ms. Fisher Miller, alternatives to evolutionary theory proposed by its critics, such as intelligent design, seem an artificial way to use science to explain the holy. "It's arrogant to say that either religion or science can answer all our questions," she said. "I don't see the need either to banish one or the other or to artificially unite them."

Gretchen Ruethling contributed reporting for this article.