(Reuters) - When televangelist Silas Malafaia gathered 40,000 followers outside Brazil's Congress this week, it wasn't just to raise their arms to the sky and praise the Lord.
The rally was a show of support for lawmakers who oppose abortion and same-sex marriage and a message to other politicians that they should not ignore Brazil's fast-growing evangelical churches if they want to stay in office.
"Gay activism is moral garbage," Malafaia roared into the microphone to a cheering crowd on the grassy esplanade of the Brazilian capital. "Satan will not destroy our family values."
The rise of evangelical Christians as a conservative political force in Latin America's largest nation has put the ruling Workers' Party on guard and led President Dilma Rousseff - who is seeking re-election in 2014 - to appoint an evangelical bishop to her cabinet.
The growing clout of evangelical churches is also bringing social and moral issues such as abortion to the center of the national agenda, some say at the expense of political and economic reforms needed to restore robust growth to the world's seventh-largest economy.
Pentecostalism was introduced to Latin America by U.S. missionaries a century ago and has gained masses of followers in recent decades in countries like Brazil, especially among the urban poor who feel neglected by the dominant Catholic Church.
With their vibrant preaching, emotional prayer and singing, evangelical Protestant churches appeal to Brazilians more than the liturgical masses of the Catholic Church. They also use electronic and social media more effectively to proselytize.
Many Brazilians who join evangelical congregations say their new religion has brought meaning to their lives, that they no longer identified with the Catholic Church.
Brazil is the world's largest Catholic nation and Pope Francis will travel to Rio de Janeiro next month on his first trip abroad as pontiff, in part to try to reverse the exodus away from Catholicism.
The Catholic Church is losing followers across Latin America - even among Hispanics in the United States - and opinion polls in Brazil point to the Church's strict positions on sex and divorce as contributing factors.
A Datafolha survey in March found 58 percent of Brazilians believe the Catholic Church should accept divorce and 83 percent believe the use of condoms should be allowed, two issues where the Vatican has refused to budge and evangelical churches are more flexible, allowing followers to decide for themselves.
One in four Brazilians is an evangelical Christian today and their churches have multiplied and become wealthy institutions that own radio and television networks, finance political campaigns and even fund their own political parties.
While Catholic priests are banned from running for public office, evangelical churches actively encourage their pastors to engage in politics and often use the pulpit to persuade their followers who they should vote for.
"Today there are 44 million mainly Pentecostal evangelicals in Brazil, which is a large social force. Obviously, this was going to change things in Congress," said Fernando Altemeyer, a former Catholic priest who teaches theology at the Catholic University of Sao Paulo.
In the last national election in 2010, evangelicals increased their presence in Congress by 50 percent and now have 68 seats in the Chamber of Deputies and three in the Senate. Though belonging to a dozen different parties, evangelicals have begun to act as a caucus in Brazil's fragmented legislature where only the farm lobby tends to speak with one voice.
The evangelical presence in Congress has been very much in the public spotlight since one of its members, a conservative preacher known for his racist and anti-gay statements, was named chairman of the chamber's Human Rights and Minorities Committee.
Pastor Marcos Feliciano, of the Social Christian Party, once stated that John Lennon's murder was divine retribution for saying the Beatles were more famous than Jesus Christ.
The committee's sessions have been disrupted almost daily by demonstrators demanding Feliciano's ouster. He has ordered guards to remove the protesters and closed the committee to the public. Congressmen from Rousseff's Workers' Party walked out, saying he was unfit to be chairman.
His backers say the longer the controversy lasts, the more votes evangelical candidates will get in the next election because he is defending traditional family values.
"He got 200,000 votes in the last election. Well, he won't get less than 500,000 next time," Malafaia said in an interview before his rally in Brasilia on Wednesday. "He's on a roll."
"The Workers' Party is going to suffer in the next election because of the evangelical vote," Malafaia predicted.
Rousseff has every reason to worry. In 2010, evangelical voters helped force the election to a runoff after abortion became a big issue late in the campaign and many votes went to her Green Party rival, Marina Silva, an evangelical Christian.
Last year, Rousseff named evangelical bishop Marcelo Crivella as her fisheries minister, even though he admitted publicly he knew little about fishing. Crivella is nephew of Edir Macedo, founder of the Universal Church of the Kingdom of God. Bishop Macedo, a billionaire who owns the TV Record network, has 5 million followers and is a hugely influential power broker in Brazil.
"Rousseff is not going to do anything that would alienate the evangelicals," said David Fleischer, political science professor at the University of Brasilia. "No candidate in their right mind would do that."
(Editing by Kieran Murray and Eric Walsh)