WASHINGTON (CNN) -- GOP presidential hopeful Fred Thompson will get the endorsement of the National Right to Life Committee, three GOP sources told CNN.
The formal announcement, which will take place Tuesday morning in Washington, is a much needed boost for Thompson's campaign, which is suffering from low poll numbers and criticism the candidate lacks enough passion to win.
Thompson, a former Republican senator from Tennessee, came into the race late with the hope of winning over social conservatives unsatisfied with the rest of the GOP field.
Although polls and anecdotal evidence suggest he's failed to excite those conservatives, he is making a big push to play up his conservative credentials on the stump and on TV. Thompson is especially emphasizing his anti-abortion views and voting record in the Senate.
Thompson has, however, faced criticism from some conservatives for what they see as conflicting statements; like his statement last week that he does not support an anti-abortion constitutional amendment -- a Republican platform position since Ronald Reagan. Thompson said he hopes Roe v. Wade will be overturned, but that in general he believes abortion laws should be left to the states.
The National Right To Life Committee boasts affiliates in all 50 states with over 3,000 local chapters nationwide. Although some GOP strategists say its grassroots power may not be as strong as it was in the past, it will likely mobilize some crucial support for Thompson's campaign.
Republican presidential candidates are battling for support from the socially conservative wing of the party, often citing endorsements from leading evangelical figures.
In a surprise move Wednesday, television evangelist and Christian Coalition founder Pat Robertson endorsed Republican White House hopeful Rudy Giuliani for president.
In a joint appearance in Washington, Robertson said he is endorsing Giuliani because he is "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.
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 Republican 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 socially 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 concerns by some about 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.
Also last week, former White House hopeful Sen. Sam Brownback, a Kansas Republican who is the leading voice for Christian conservatives in the Senate, endorsed Sen. John McCain from Arizona.
Brownback 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.
McCain opposes legalizing abortion and gay marriage, but he is not a darling of the far right. Brownback is a socially conservative senator who emphasized his opposition to abortion, gay marriage and other issues important to Christian conservatives.
His endorsement could help McCain in Iowa, where he trails badly in the polls to Romney. The Iowa caucuses kick off the presidential primary calendar January 3. E-mail to a friend
CNN's Dana Bash, John King, and Mark Preston contributed to this report