Boston ? Sen. Sam Brownback argues he’s the true conservative in the race for the 2008 Republican presidential nomination, while former Massachusetts Gov. Mitt Romney may have trouble explaining flip-flops in his background.

“I think you have to look at where he stood on the issues and what he said publicly,” the Kansas Republican told the Christian Broadcasting Network in an interview published Wednesday. “At times he’s said different things on these issues. I think that’s all going to come out during a long campaign.”

Romney, for example, ran for governor in 2002 touting his support for abortion rights; now he highlights his opposition to abortion. Social conservatives have also expressed concern about him declaring in 1994 that he would be a better activist for the gay agenda than his then-opponent, Sen. Edward M. Kennedy, D-Mass. Romney now touts his opposition to gay marriage.

“If you look at our lineup right now, I’m the solidly pro-life candidate and I’ve worked on these issues, believe in them and have a base of support,” Brownback said. “I do think when we get out on the campaign trail and when the campaign really gets fully engaged, there’s going to be a lot of discussion about where do people actually stand on the issues and where have they been and where are they now and how reliable are they to stay that way.”

Romney spokesman Kevin Madden said: “As governor, he’s been a champion of traditional marriage. He’s fought the efforts of activist judges who seek to redefine marriage, and he’s testified before the U.S. Senate in support of the Federal Marriage Amendment.”