* Perry polishes credentials for religious conservatives
* Texas governor offers prayer for nation at rally
* Organizers estimate crowd at 30,000
(Adds end of rally, new Perry quote, reaction, details)
By John Whitesides
HOUSTON, Aug 6 (Reuters) - Texas Governor Rick Perry, expected to enter the Republican race for the White House within weeks, offered a prayer for America on Saturday at a controversial religious rally that put the spotlight on his Christian faith.
Perry, who has made his religious beliefs a big part of his public image, urged an enthusiastic crowd at the seven-hour gathering to pray for President Barack Obama and other U.S. leaders.
"Father, our heart breaks for America," said Perry, who hatched the idea for the rally and brushed off heavy criticism for participating.
"We see discord at home, we see fear in the marketplace, we see anger in the halls of government. As a nation, we have forgotten who made us," Perry said in a prayer offered to a crowd estimated by organizers at more than 30,000 people.
The event was named "The Response" and billed as a day of prayer for a nation in crisis. It also gave Perry a national platform to sharpen his appeal to religious conservatives who play a big role in the Republican nominating race and have been unhappy with the current crop of contenders.
Sponsors of the rally included the American Family Association, whose leaders have condemned gays and Muslims, and the International House of Prayer, founded by an evangelist who warns celebrity Oprah Winfrey is a pastor in a Satan-inspired religion.
It also drew prominent religious conservative leaders such as Focus on the Family head James Dobson and Tony Perkins of the Family Research Council.
Critics condemned the event for excluding non-Christian faiths and blurring the boundary between church and state, as well as affiliating with controversial fringe religious groups and leaders.
"Governor Perry achieved his goal today -- he drove almost every religious right leader and group into his corral," said Reverend Barry Lynn, executive director of Americans United for Separation of Church and State.
Perry is poised to enter the 2012 Republican presidential race in the next few weeks. He already has shot into the top tier of contenders in opinion polls.
At the rally in Houston's cavernous 70,000-seat Reliant Stadium, home of the Houston Texans professional football team, Perry discussed his faith, read scripture and said a prayer.
"We know the greatest darkness comes just before the morning," he said in a 12-minute appearance, adding God was wise enough to avoid affiliation with any political party.
"His agenda is not a political agenda. His agenda is a salvation agenda," said Perry, who was criticized for blending politics and religion in launching the prayer rally.
'A CAMPAIGN PROP'
"This isn't the first time we have seen Governor Perry use a religious gathering or house of worship as a campaign prop," said Kathy Miller, executive director of the Texas Freedom Network, a nonpartisan watchdog on far-right religious groups.
Perry closed the event by saying he hoped it would begin a national renewal and "our willingness to stand in the public square" would inspire others to seek God.
The rally had a mix of Christian rock, testimonials and scripture from pastors and children, as well as numerous calls to end abortion but little other overtly political rhetoric.
Participants said they were praying to heal a troubled nation and politics was not their concern. Many in attendance, who came in church buses from throughout the region, praised Perry for leading the effort.
"He was brave enough to stand up and say, 'Hey, we've got to pray for the nation.' He's the governor but he's a Christian man," said Lonnie Lavender, a pastor at the War Cry Prayer Ministry in Venus, Texas.
Eddie Ellis, a delivery service owner in Conroe, Texas, who bused to the event with about 50 parishioners from his church, said Americans needed to "wake up."
"Perry is a politician but he says we've got to pray. He hits the right keys," Ellis said.
Perry invited all of the nation's governors but Republican Sam Brownback of Kansas was the only one to attend. Florida Governor Rick Scott, also a Republican, sent a video message.
The event was broadcast on the Internet to more than 1,000 churches around the country, sponsors said. Organizers draped black curtains behind the stage to hide empty seats, although the crowd was larger than predicted earlier in the week.
Perry's emphasis on his Christian faith could be a drawback in a general election when it could turn off moderates and independents, along with those of non-Christian faiths.
(Editing by Xavier Briand and Bill Trott)