WASHINGTON (CNN) -- Call it a battle for the hearts and minds of Christian conservative voters.
Pat Robertson, right, endorses Rudy Giuliani Wednesday in Giuliani's quest to be the GOP presidential nominee.
Pat Robertson, the television evangelist and Christian Coalition founder, endorsed Republican White House hopeful Rudy Giuliani for president when the two men appeared together at the National Press Club in Washington on Wednesday.
Robertson said he decided to endorse Giuliani because he was "a proven leader who is not afraid of what lies ahead and who will cast a hopeful vision for all Americans."
"In all of the crises which confront our nation and the world, we need a leader with a bold vision who is not afraid to tackle the challenges ahead," Robertson said. Watch Robertson call Giuliani ready to lead »
Meanwhile, former White House hopeful Sen. Sam Brownback, a Kansas Republican who is the leading voice for Christian conservatives in the Senate, will endorse Sen. John McCain for president, McCain's campaign announced Wednesday.
The Giuliani campaign hopes the Robertson endorsement will help the former New York City mayor to make inroads among evangelical Christians. Giuliani is trying to make the case with social conservative voters that despite his support for abortion and gay rights, he is an acceptable choice as the Republican presidential nominee.
It was Robertson's 1988 presidential campaign that, while unsuccessful, established evangelical voters as a dominant force within the Republican Party.
Robertson has repeatedly praised Giuliani despite their major differences on social policy. Both men say a friendship developed after a long conversation on a plane during a trip to Israel several years ago. Another thing both men have in common is that they are prostate cancer survivors.
Giuliani is the frontrunner in the national polls, but he trails in surveys in many of the early primary and caucus states, among them Iowa and South Carolina, where social conservative voters make up a major part of the Republican voting electorate.
The Robertson endorsement may also quash talk of a social conservative third party candidate if Giuliani wins the nomination.
It also put a dent in Mitt Romney's courting of the religious right. The former Massachusetts governor has made major inroads with Christian conservatives, despite the concerns by some regarding his Mormon faith.
When asked about Robertson's endorsement, Romney said, "You can't get them all" and then touted his recent endorsements from conservative activist Paul Weyrich and Bob Jones III, the president of the evangelical Bob Jones University in Greenville, South Carolina.
McCain is also hoping to capture Christian conservative support. A McCain campaign source and Republican Party sources tell CNN that Brownback's endorsement will come today when the two men appear together at a McCain campaign event in Iowa.
The Republican senator from Kansas gave up his own bid for the White House last month after lackluster fundraising and poor showings in both the national and crucial early primary and caucus state polls.
"I am endorsing the best pro-life candidate to beat Hillary Clinton," Brownback said in a press conference in Dubuque, Iowa.
"Here is a pro-life leader who will appoint strict-constructionist judges so that I believe we can end this night of wrong and have Roe v. Wade overturned," Brownback continued.
McCain, who hovers around fourth place in many recent polls out of this crucial early-voting state, hailed the endorsement as "significant."
"There are endorsements and then there are endorsements, support and different kinds of support," he said. "This time the support comes from one of the most respected men in America."
Brownback is a socially conservative senator who emphasized his opposition to abortion, gay marriage and other issues important to Christian conservatives, who make up an influential voting block within the Republican Party.
His endorsement could help McCain in Iowa. The caucuses there, which will be held on January 3, will kick off the presidential primary calendar.
McCain trails badly in the polls in Iowa to Romney. McCain opposes legalizing abortion and gay marriage, but he is not a darling of the far right. Brownback's endorsement may help McCain with such social conservative voters. E-mail to a friend
CNN's John King, Peter Hamby and Alexander Mooney contributed to this report.