It was billed as a day of prayer and fasting to halt America's national decline, and about 30,000 answered the call, flooding into Houston's Reliant stadium for a seven-hour marathon which blended Christian revivalism with hard-headed electoral campaigning.

There was plenty of prayer: some of the faithful stood with arms held high in supplication, others danced trancelike in the aisles and still more lay spreadeagled on the floor.

The fasting was less conspicuous: long queues formed at Prince's Hamburgers, Tejas Nachos, Five Star Dogs and other fast-food stands inside the cavernous arena.

The rally on Saturday marked another step towards the launch of Rick Perry's presidential campaign, giving the governor of Texas a national platform for the first time, with 250 reporters and camera crews covering it.

More importantly, it virtually guaranteed him the support of the Christian evangelical movement, with its network of volunteers and finance, plus a large bloc of votes in Republican caucuses and primaries.

Perry, 61, who is in his third full term as governor, has still not officially announced his candidacy for the Republican nomination. But whenever he does – he is expected to declare his intentions this month – he will likely become the frontrunner for the nomination to take on Barack Obama next year.

"I would vote for him. I would vote for him out of all the Republican candidates," said Buzz Park amid an audience which included youth groups, soccer moms and Christian bikers. "He is not afraid to say this is a problem and this is how to fix it. Obama is not a leader."

Park said America was in decline economically and morally, and losing its influence abroad. "The nation that forgets God is turned into hell," he said. God had promised that through prayer this could be reversed, healing the land. Had this been successful before? Park cited Fiji in the 1990s and revivalist meetings in Wales around 1900.

The rally originated in December when Perry called for Christians across the US to join him in Houston and invited the other 49 state governors to attend. Organisers put the attendance at about 30,000, less than half the capacity of the 71,000-seater stadium. The only other governor to turn up was Sam Brownback from Kansas.

The turnout was higher than some had expected but was still quite low given that Houston is the fourth-largest city in the US and a large proportion profess to be Christian. Some of America's megachurches attract 30,000 or more every Sunday. But Perry showed no sign of disappointment. He seemed happier and more enthusiastic preaching in Houston than he had when delivering a political speech at the Republicans' southern conference in New Orleans in June. He finished his 13-minute sermon with a smile and a clenched fist.

"Father, our heart breaks for America. We see discord at home. We see fear in the marketplace. We see anger in the halls of government, and as a nation we have forgotten who made us, who protects us, who blesses us, and for that we cry out for your forgiveness," Perry said.

His rhetorical style is derived from the tent preachers of the Old West, and the crowd stood enthusiastically throughout, responding with amens.

Much of secular and liberal America watches anxiously at the prospect of another Texas president tied to the Christian evangelical movement. That unease is shared by progressive Christians who fear Perry is identifying with the most conservative church leaders.

The American Family Association (AFA), which runs a network of 200 radio stations – and which has been labelled a "hate group" by the Southern Poverty Law Centre for its attitude to gay people – contributed an estimated $1m towards the cost of the rally.

The Cornerstone Church – whose leader, John Hagee, gained notoriety for declaring that Hurricane Katrina was God's vengeance on a sinful New Orleans and suggesting that Jews had brought the Holocaust on themselves – sent about 700 members, travelling from San Antonio by car and bus.

Elva Spoor said she had come with the Cornerstone delegation so "God can bless us and give us rain and turn the nation back to God". But what about gay people? "God says he loves everyone but he hates the sin," said Spoor. "God says it is an aberration to him."

John McCain, the previous Republican presidential candidate, had an uneasy relationship with Christian evangelicals, initially ignoring them and then seeking out their support. But he drew the line at Hagee and refused to accept his endorsement.

Until a last-minute change of running-order, Hagee was scheduled to speak directly after Perry. Hagee steered away from controversial subjects and offered prayers for the nation's leaders, before comparing Perry to Abraham Lincoln.

"We pray for our governor Rick Perry who has had the courage today to call this time of fasting and prayer just as Abraham Lincoln did in the darkest days of the civil war," Hagee said.

The event provoked a backlash in Texas, including a lawsuit by atheists aimed at stopping it, charging that Perry was in breach of the separation of politics and religion. On Saturday, a plane flew over the stadium with a banner with the same message about separation of politics and religion. Other Christian churches held alternative prayer meetings on Friday and Saturday.

Among about 150 protesters outside the stadium was Pastor Katherine Godby. Carrying a poster saying "Hate Is Not A Gospel Value", she expressed sadness that Perry had aligned himself with the AFA.

Godby, of the First Congregational United Church of Christ in Fort Worth, said: "We see their portrayal of the gospel as one of exclusion and hatred."

Jennifer Stephenson, a mother of three from San Antonio carrying a "Christians Against Perry" placard, described the attitude of groups such as the AFA as "un-Christian".

She was worried that disillusionment with Obama among leftwing voters might open the way for a possible Perry presidency. "I think Perry has a good chance, unfortunately. He is good-looking, brought a lot of jobs to this state and has got a lot of Christians behind him," she said. "The Christian voting bloc is a force to contend with."

Perry's previous attempts to invoke a higher power suggest that there are limits to the power of prayer. In April, he declared a three-day vigil for rain in Texas. But those prayers have so far gone unanswered, and the state is still suffering its worst drought since 1895.