ANOKA, Minn. — Lynn Sunde, an evangelical Christian, is considering what for her is a radical step. Come November, she may vote for a Democrat for Congress.

"You're never going to agree with one party on everything, so for me the key has always been the religion issues — abortion, the marriage amendment" to ban same-sex unions, said Sunde, 35, who manages a coffee shop and attends a nondenominational Bible church.

That means she consistently votes Republican. But, she said, she is starting to worry about the course of the Iraq war, and she finds the Internet messages from then-Rep. Mark Foley, R-Fla., to teen-age boys "pretty sickening." When she goes into the voting booth this time, she said, "I'm going to think twice. ... I'm not going to vote party line as much as to vote issues."

Even a small shift in the loyalty of conservative Christian voters such as Sunde could spell trouble for the GOP this fall. In 2004, white evangelical or born-again Christians made up a quarter of the electorate, and 78 percent of them voted Republican, according to exit polls. But some pollsters believe that evangelical support for the GOP peaked two years ago and that what has been called the "God gap" in politics is shrinking.

A nationwide poll of 1,500 registered voters released Thursday by the nonpartisan Pew Research Center found that 57 percent of white evangelicals are inclined to vote for Republican congressional candidates in the midterm elections, a 21-point drop in support among this critical part of the GOP base.

Even before the Foley scandal, the portion of white evangelicals with a "favorable" impression of the Republican Party had fallen sharply this year, from 63 percent to 54 percent, according to Pew polls.

In the latest survey, taken in the last 10 days of September and the first four days of October, the percentage of evangelicals who think that Republicans govern "in a more honest and ethical way" than Democrats has plunged to 42 percent, from 55 percent at the start of the year.

In Minnesota's conservative 6th Congressional District, the loosening of the GOP's hold on religious voters is helping Patty Wetterling, an anti-war Democrat, run an unexpectedly close race against Republican state Sen. Michele M. Bachmann, who has made opposition to abortion and same-sex marriage her signature issues. This week, Wetterling became the first Democrat in the country to air a TV advertisement about the Foley scandal.

Wetterling is best known as an advocate for missing children. Her 11-year-old son, Jacob, was abducted in 1989 and never found. The uproar over Foley's sexual correspondence with teen-age employees of Congress has played into her political strength.

"This is something we all watched with churches years ago, where they didn't do anything. Congress has no excuse — they know better," she said.

The incumbent, Rep. Mark Kennedy (R), is vacating his seat to run for the Senate. The national GOP has spared no effort to bolster Bachmann. President Bush, Vice President Dick Cheney, political strategist Karl Rove, House Speaker J. Dennis Hastert, R-Ill., and Commerce Secretary Carlos M. Gutierrez all have been out to campaign for her.

Unlike some Republican candidates across the country, Bachmann is not running away from Bush. She says she is "thrilled" to be associated with him.

But the president's ratings have slipped even within his most loyal constituency. Since the start of his second term, Bush's favorability rating has dropped from 52 percent to 42 percent among all adults, and from 71 percent to 60 percent among white evangelical Protestants, according to Washington Post-ABC News polls.

"I think he's too set in his way to listen to what's really going on in Iraq," Sunde said. She noted that her rising concern about the war "possibly could" lead her to cross party lines and vote for Wetterling.

"If you're pro-life and mad about the war, where do you go? That's the Bachmann-Wetterling race in a nutshell," said state Rep. Jim Abeler, 52, a Republican who represents part of the 6th district.

Jim Bernstein, 56, a Democrat who served as Minnesota's commerce commissioner under then-Gov. Jesse Ventura, agreed: "There are a lot of people here who say, 'I'm pro-life, but I'm also concerned about healthcare, about education, about jobs.' "

Across the country, many Democratic candidates are wooing religious voters by talking about their faith. Wetterling is not among them. Her campaign manager calls her "a very spiritual woman," but says: "We have her all over the district now, so much so that she's not able to attend church."

Bachmann, on the other hand, attends an evangelical megachurch and is known for her unsuccessful effort to put a state constitutional amendment against same-sex marriage on the November ballot. If same-sex marriage spreads, she has warned, "public schools would have to teach that homosexuality and same-sex marriages are normal, natural and that maybe children should try them."

Nationally, the Republicans' once formidable hold on churchgoing voters has begun to slip. Among those who say they attend church more than once a week, the GOP still holds a commanding lead. The main shift is among weekly churchgoers, about a quarter of all voters. Two years ago, they favored the GOP by a double-digit margin. But in the new Pew survey, 44 percent leaned toward Republicans and 43 percent toward Democrats, a statistical dead heat.

The slippage is particularly striking among evangelicals. According to Pew data, the portion of white evangelical Protestants who identify themselves as Republicans rose steadily from 2000 to 2004 but leveled off this year at about half. The percentage who support keeping troops in Iraq has dropped to 55 percent, from 68 percent in early September.