Six GOP hopefuls joined a policy forum on Fox News Saturday night to push their conservative credentials, with Newt Gingrich seeking to reassure voters and vowing that he would reject "big government approaches" if elected president.

In the televised forum, hosted by former Arkansas Gov. Mike Huckabee, candidates answered questions from three Republican state attorneys general: Pam Bondi of Florida, Oklahoma's Scott Pruit and Ken Cuccinelli of Virginia.

The forum was attended by Gingrich, former Massachusetts Gov. Mitt Romney, Reps. Ron Paul (Texas) and Michele BachmannMichele Marie BachmannTom Petty dies at 66 Bachmann: Muslim immigrants trying to undermine Western civilization Religious leaders pray over Trump in Oval Office MORE (Minn.), Gov. Rick Perry (Texas) and former Sen. Rick Santorum (Penn.)

Gingrich who has risen to the top of many GOP polls after a series of strong debate performances and stumbles by his rivals faced questions about his past support for government policies addressing climate change and in favor of a healthcare insurance mandate.

Gingrich pledged that conservative voters could "trust that a President Gingrich will not advance these sorts of big government approaches."

The former House speaker said his past support for a mandate had been consistent with what other conservatives had believed at the time. "Every conservative has in fact left that kind of a model," said Gingrich.

Gingrich also faced tough questioning from the panel on immigration policy and stood by his recent proposals to allow some families of undocumented workers to remain in the country.

“I’m suggesting that this only apply to people who’ve been here a very long time, who have a real tie to the local community, and we’re exploring the idea that they’d actually have a family sponsoring them,” he said.

Gingrich has received criticism from anti-illegal immigration activists and his presidential rivals who have labeled his plan "amnesty."

During the forum, the presidential candidates interacted with the panel individually and did not interact with each other.  However, each took the opportunity to stress that they would hew to conservative principles more closely than their opponents.

Texas Gov. Rick Perry pulled a copy of the constitution from his pocket and said that would guide his policies if elected. "Read it, exactly what it says. That's what we're talking about," said Perry.

The forum comes as a new poll shows Gingrich leading in Iowa. The latest Des Moines Register poll released Saturday night shows Gingrich winning the support of 25 percent of likely GOP caucus-goers surveyed, ahead of Rep. Ron Paul (Texas) with 18 percent and ahead of Mitt Romney with 16 percent support.