WASHINGTON (CNN) -- Republican presidential hopeful Mitt Romney blasted a rising challenger in the Iowa caucuses Monday, painting former Arkansas Gov. Mike Huckabee as a tax-raising, illegal immigrant-coddling liberal and defending his own commitment to conservative causes.
Mitt Romney campaigns in Norton, Iowa, last week.
"He may be conservative on social issues, but when it comes to economic issues like immigration, he's a liberal on immigration. He fought for tuition breaks for illegal aliens. He raised taxes time and time again as governor of Arkansas," Romney told CNN.
Romney has long been the frontrunner in Republican polls in Iowa, but surveys in the past two weeks indicate that Huckabee has closed the gap with the former Massachusetts governor.
With just six weeks before the first contest of the 2008 presidential race, both men have draped themselves in the mantle of former President Ronald Reagan.
"I must admit that I find the vision and the direction that Ronald Reagan laid out for this country to be very powerful and very compelling," Romney said. "And I'll tell you, Ronald Reagan would have never raised taxes like Mike Huckabee did.
"Ronald Reagan would have never said let's give tuition breaks to illegals like Mike Huckabee did. Ronald Reagan would have never stood by and pushed for a budget that more than doubled during his term as president."
Sunday, Huckabee pointed out that Romney's opposition to abortion, gun control and gay marriage were fairly recent -- and said those changing views were a major reason why the polls have tightened in the Hawkeye State.
"When he was pro-abortion, I was still pro-life and always have been," Huckabee told CNN. "When he was for gun control, I was against it. When he was against the Bush tax cuts, I was for them. When he was against Ronald Reagan's legacy and said he wasn't part of that Bush-Reagan thing, I was a part of that Bush-Reagan thing."
Romney shot back Monday that Reagan, a conservative icon, did not oppose abortion until after he was governor of California in the 1960s. Romney has said his study of policies involving embryonic stem cell research prompted him to reverse his earlier support for abortion rights while running for governor of Massachusetts. Watch Romney defend his record »
"I'm very proud of the fact that I became pro-life, just like Ronald Reagan did," he said. "When theory met reality when I became governor, every action I took as governor came down on the side of life."
Huckabee has drawn interest with his low-key, sometimes humorous style on the campaign trail -- including a recent endorsement by action star Chuck Norris, who appears with Huckabee in a video ad airing in Iowa. But he is facing tougher scrutiny in conservative circles as he gains ground.
Columnist Robert Novak blasted him as a "false conservative" in his syndicated column Monday, and the Club for Growth, a hard-line anti-tax group, said his victory would be an "abject rejection" of GOP principles.
Romney has a wider lead in New Hampshire, which holds its primary five days after Iowa's January 3 caucuses.
But he has faced new criticism of his judicial appointments as governor from former New York Mayor Rudy Giuliani, who trailed Romney and Arizona Sen. John McCain in a CNN/WMUR poll out last week.
Last week, Romney called for one of his appointees to resign for releasing a convicted murderer who is now facing charges of killing a Washington state couple. Monday, he said it was "strange" for Giuliani to bring up the issue "when he's got Bernie Kerik all over him these days."
"Someone he knew was under investigation, he recommended to the president to be secretary of homeland security?" Romney said. "Throwing stones from a glass house is never a wise thing to do."
Kerik served as New York's police commissioner and corrections chief during Giuliani's two terms as mayor, and President Bush named him to the Cabinet post in 2004. Questions about his finances forced Kerik to withdraw his nomination within weeks.
In 2006, Kerik pleaded guilty to misdemeanor charges of accepting tens of thousands of dollars in gifts while he worked as corrections commissioner. He paid a $221,000 fine and avoided jail time -- but a federal grand jury brought new charges of tax fraud, conspiracy and making false statements to federal officials earlier this month.
Prosecutors said Kerik received about $255,000 in renovations to his apartment from a company seeking to do business with the city of New York and concealed the income from the Internal Revenue Service. Kerik has pleaded not guilty to the charges. E-mail to a friend
CNN's Paul Steinhauser contributed to this report.