Press Secretary Scott McClellan told reporters, "No one that knows her would make such a suggestion."
Leading conservatives have voiced doubt that Miers — who's never been a judge and has little public record — is the best qualified for the job. And some have called on the White House counsel to bow out.
In a testy exchange with reporters, the spokesman complained that the nomination has become embroiled in "side issues like religion."
Democrats raised alarms after the administration acknowledged it's been assuring top conservatives that Miers is a "person of faith" who attends a staunchly anti-abortion church.
Bush defended his nomination Wednesday, saying Miers was highly qualified, a trailblazer in the law in Texas and someone who would strictly interpret the Constitution, something his conservative supporters desire.
He said his advisers' comments about Miers' churchgoing were meant to give people a better understanding of his little-known nominee.
"People are interested to know why I picked Harriet Miers," he said. "They want to know Harriet Miers' background. They want to know as much as they possibly can before they form opinions. Part of Harriet Miers' life is her religion."
That comment further inflamed critics of the nomination who contend Miers' religion is being used to sell the nominee to the right flank of Bush's conservative base. They argue that the president is asking them to trust him and blindly support his nomination even though Miers has no judicial record that would offer insight into how she would vote on the high court.
On a radio show broadcast Wednesday, James Dobson, founder of the conservative Focus on the Family, said that before Miers was nominated, deputy White House chief of staff Karl Rove reassured him that she was an "evangelical Christian, that she is from a very conservative church, which is almost universally pro-life."
The strategy comes just weeks after the White House said the religious views of his first nominee, John Roberts, should not be an issue, reports CBS News correspondent Peter Maer.
"The White House and the religious right leaders rallying around the beleaguered nomination of Harriet Miers continue to cite her religious beliefs and the church she attends as reasons to believe she will oppose abortion rights and to bolster support for her among activists on the far right," said Ralph Neas, director of the liberal People for the American Way. "What's wrong for John Roberts can't be right for Harriet Miers."
The Rev. Barry Lynn, director of Americans United for the Separation of Church and State, said anyone who tried to bring up the topic of religion during the Roberts confirmation was labeled a bigot. "Now Bush and Rove are touting where Miers goes to church and using that as a selling point," Lynn said. "The hypocrisy is staggering."
A little over a week since Miers was nominated, complaints continued from the right. Other conservatives, however, jumped into the fray to support Miers.
Religious broadcaster Pat Robertson, who has endorsed Miers, issued a warning to conservative senators who might be thinking of voting against her. "They're going to turn against a Christian who is a conservative picked by a conservative president and they're going to vote against her for confirmation? Not on your sweet life, if they want to stay in office," he said.