When Texas Gov. Rick Perry got the idea of holding a big Christian prayer rally after winning his third term last November, running for president was barely a blip on his radar screen.

Now, in all likelihood, Governor Perry will launch a presidential campaign by the end of the month, and “The Response: A Call to Prayer for a Nation in Crisis” has arrived. On Saturday, Houston’s Reliant Stadium will host 8,000 people, including prominent religious leaders – some of them controversial. All the nation’s governors were invited, but only one accepted: Sam Brownback (R) of Kansas, and his attendance is in doubt.

The evangelical Perry will be present for the entire seven-hour event, and plans to speak. As a political event, Perry’s prayer summit could pay dividends in the race for the Republican presidential nomination. Religious conservatives form a critical part of the GOP’s activist base, and he could steal votes from other evangelical Christians in the field, including the two Minnesotans, Rep. Michele Bachmann and former Gov. Tim Pawlenty.

“I don’t think [the rally] will hurt him in the primaries; in fact, it might even help him,” says John Green, an expert on religion and politics at the University of Akron in Ohio. “But were he to get the Republican nomination, this kind of event could become controversial.”

Certainly, prayer breakfasts featuring politicians – including the president – are common. But the conservative Christian focus of the event, in which leaders of Catholic, Jewish, mainline Christian, and other faiths were not invited to speak, has raised objections. On Aug. 2, the Anti-Defamation League released a letter signed by 50 clergy of a variety of faiths, objecting to what they call Perry’s “day of exclusionary prayer.”

On Friday night, the Texas American Civil Liberties Union and Americans United for Separation of Church and State are holding an alternate “Family, Faith, and Freedom” event, featuring speakers from religious and nonreligious groups.

Organizers of “The Response” say that all are welcome to attend their event.

Some of the people involved, says Mr. Green, are “very conservative voices even among conservatives.” And that’s where the event could become controversial.

One figure involved, Pastor John Hagee of Cornerstone Baptist Church in San Antonio, Texas, said after hurricane Katrina that “New Orleans had a level of sin that was offensive to God,” and thus received “the judgment of God.” He later backed away from the comment. Still, 2008 GOP presidential nominee John McCain turned down Pastor Hagee’s endorsement.

Another religious figure involved in the event, Mike Bickle of the International House of Prayer in Kansas City, Mo., has called Oprah Winfrey the “Antichrist.”

The group organizing the event, the American Family Association, condemns homosexuality, and in 2005 was designated a “hate group” by the Southern Poverty Law Center.

The prayer rally is turning into both more and less than what it was intended to be, says Cal Jillson, a political scientist at Southern Methodist University in Dallas.

“It’s less, in the sense that I think they expected a significant number of Republican governors to come and lend real prestige and visibility to him, and help jump-start a Perry campaign,” says Mr. Jillson. “It’s more, in the sense that people who do not know Rick Perry are going to form a judgment on him based on what happens this weekend.”

Some political observers have suggested that since it’s early in the presidential cycle, the faith rally will have receded in memory by the time voters go to the polls. But in this case, the event could go either way for Perry – positive or negative – and if it’s the latter, the rally will live on in perpetuity on video.

“If what the public sees is a bunch of well-intentioned Christians praying for their country, even if it makes people on the left nervous, that’s a win for Perry,” says Jillson. “If the public sees wild-eyed people calling somebody out for the moral decline of the country, then you’re in a whole different area.”