DENVER — He is a child psychologist who heads a conservative Christian ministry some 1,500 miles from Washington, but James Dobson's vast radio audience and White House ties have made him a key player in the fiery debate over Harriet Miers' nomination to the Supreme Court.

Dobson, founder of the Colorado Springs-based Focus on the Family, drew attention last week when he said Karl Rove, one of President Bush's most trusted advisers, had told him things about Miers "that I probably shouldn't know."

Amid intense pressure to reveal what he knew, Dobson this week said Rove had merely told him that Miers was an evangelical Christian with ties to the anti-abortion movement, and that Rove had spoken to him before Bush announced Miers' nomination.

That episode, combined with Dobson's willingness to endorse Miers when many other prominent conservatives held back, have put him in the middle of the argument over Miers' nomination.

"I think what it represents is the fact that Dobson is a voice that reaches a large portion of the Bush base, a very crucial base," said Corwin Smidt, a political scientist at Calvin College in Grand Rapids, Mich., and director of the Institute for the Study of Christianity and Politics there.

Dobson's aides, who in the past have seemed to downplay any ties between Focus on the Family and the White House, now say the Bush administration listens to him. "Obviously the White House considers his voice to be important," said Tom Minnery, Focus on the Family's vice president for government and public policy.

Last spring, Minnery had said Focus participates in occasional conference calls with White House officials, but "it's not even Karl Rove. It's lower-level people."

In an interview Thursday, Minnery said the Rove-Dobson conversation about Miers was not the first time the men had spoken.

"He's talked to Karl before," Minnery said. He declined to discuss their other conversations, referring those questions to Dobson — who was unavailable for comment, officials at Focus on the Family said.

Senate Judiciary Chairman Arlen Specter has said he or the Judiciary Committee's top Democrat, Vermont Sen. Patrick Leahy, could call Dobson to testify about his communication with the White House.

Dobson, who holds a Ph.D. in child development, founded Focus on the Family in Arcadia, Calif., in 1977. It has grown to a 1,300-employee operation now based in Colorado Springs, and says its radio shows and publications reach more than 200 million people worldwide.

Dobson's goal, according to the group's Web site, is to " 'turn hearts toward home' by reasonable, biblical and empirical insights so people will be able to discover the founder of homes and the creator of families: Jesus Christ."

He has publicly staked out conservative positions on issues such as stem cell research and abortion, making him a favorite of the right and a frequent target of the left.

Smidt rates Dobson as one of the nation's most influential religious conservatives. "It would appear to me there are relatively few that have the kind of influence Dobson does, partly because of the vast radio network Dobson has," he said.

Dobson's support for Miers is important, Smidt said, especially because so many other conservative leaders have voiced reservations or even opposed her. Dobson "allows evangelical Christians to come to support her nomination," Smidt said.