Eric Gay / AP Photo

ABC News' Michael Falcone and Shushannah Walshe report:

SIOUX CITY, Iowa - The harsh attacks leveled by the candidates, their campaigns and their allies spilled over onto a debate stage in Iowa on Thursday night, but the two leading candidates for the Republican nomination largely avoided direct combat.

Mitt Romney and Newt Gingrich turned down numerous opportunities to skewer each other, deciding instead to focus on their own closing arguments to voters less than three weeks before this state's Jan. 3 caucuses.

It wasn't for the moderators' lack of trying. When Gingrich was confronted with Romney's recent critique of him as an "unreliable leader in the conservative movement," the former House Speaker simply dismissed his rival's words as "laughable."

"It's sort of laughable to suggest that somebody who campaigned with Ronald Reagan and with Jack Kemp and has had a 30-year record of conservatism, is somehow not a conservative?" Gingrich said without ever mentioning Romney's name.

Romney also passed up several chances to inject the ferocity with which he has been hammering Gingrich on the campaign trail into the 13th debate of the primary season, which took place at the Sioux City Convention Center and was sponsored by Fox News and the Iowa Republican Party.

Asked to explain why he would be a "tougher" candidate than Gingrich to take on President Barack Obama in a general election, Romney chose not to contrast himself with the former House Speaker, but instead used the question to take on the president.

"I know what it takes to get this economy going.  The president doesn't," Romney said. "The proof is in his record. It's terrible. My record shows that I can get America working again."

All seven presidential candidates appeared on stage for the final time before the Iowa Caucuses, and the focus remained on Gingrich and Romney - the two candidates who appear to have the best chance of capturing the Republican nomination.

As was the case at last weekend's ABC News debate, Gingrich was the recipient of most of the incoming fire from his fellow GOP contenders. "It goes with being right here," Gingrich said on Thursday night referring to his position at the center of the debate stage and at the top of the primary polls.

With Gingrich and Romney keeping each other at arms length, it fell to several of the other candidates on the stage to lob the sharpest attacks.

Congresswoman Michele Bachmann led the charge against Gingrich, beginning with her accusation that the former House Speaker's consulting work for the housing giant Freddie Mac was tantamount to lobbying. When asked what evidence she had to support her claim, Bachmann replied, "he cashed paychecks from Freddie Mac.  That's the best evidence that you can have - over $1.6 million."

"And, frankly," Bachmann continued, "I am shocked listening to the former speaker of the House, because he's defending the continuing practice of Freddie Mac and Fannie Mae."

As he has before Gingrich insisted that Bachmann's assertion was "factually not true."

"I never lobbied under any circumstance.  I never went in and suggested in any way that we do this," he said. "In fact, I tried to help defeat the housing act when the Democrats were in charge of the House."

But it wasn't just Bachmann who was trying to knock Gingrich off his pedestal. Congressman Ron Paul echoed Bachmann in criticizing Gingrich for his work for Freddie Mac, saying that the money his opponent received from the mortgage giant was "literally coming from the taxpayer."

"They went broke," Paul said. "We had to bail them out. So indirectly, that was money that he ended up getting. They're still getting money from a government-sponsored enterprise. It's not a free-market enterprise."

For his part, Romney spent much of the night casting himself as a general election candidate who that just happened to be on the same stage with other members of his party vying for the same prize. His focus was, in large part, the White House, not his opponents.

Romney declined to engage Gingrich on his suggestion earlier this week that the former Massachusetts governor should give back money he made from companies that went bankrupt while he was trying to turn them around as an executive at Bain Capital.

Instead, Romney replied, "it's a great opportunity for us because I think the president is going to level the same attack."

"In the real world that the president has not lived in, I actually think he doesn't understand that not every business succeeds," Romney said. "In the real world, some things don't make it.  And I believe I've learned from my successes and my failures."

When the moderators asked Romney if he agreed with Obama's decision to try to negotiate with Iran to retrieve a downed unmanned U.S. drone, he accused the president of following a "pretty please" approach to foreign policy.

Acutely aware of the boost that a strong showing in Iowa could offer, many of the candidates sought to appeal directly to the state's Republican primary electorate. Bachmann, who has been trying to court social conservative and evangelical voters, emphasized her staunch anti-abortion rights position. Gingrich fit in a laudatory reference to the influential Iowa Rep. Steve King.

Texas Gov. Rick Perry, whose tumbling poll numbers in the primary field has largely been due to a string of poor debate performances, poked fun at himself with a comparison to an unlikely pro-football sensation.

"There are a lot of folks that said Tim Tebow wasn't going to be a very good NFL quarterback.," Perry said. "There are people that stood up and said well he doesn't have the right throwing mechanisms or he doesn't, you know he's not playing the game right, and  you know, he won two national championships and that looked pretty good, and we were the national champions in job creation back in Texas, and so but am I ready for the next level? Let me tell ya, I hope I am the Tim Tebow of the Iowa caucuses."

As the battle for the Republican primary enters its most intense phase, Fox News anchor Bret Baier, offered a closing question to the candidates: Were they worried about the consequences of breaking Ronald Reagan's 11th Commandment, which states that Republicans should not speak ill of each other?

"I've been kicked pretty hard by a lot of Iowans about the positions I hold," said former Pennsylvania Rick Santorum, who has campaigned in all of Iowa's 99 counties."The other side's going to kick very, very hard and we've got to have someone who can stand up for it, fight and holds those convictions deep so they can fight the good fight in the fall and win this presidency."

Romney insisted there has been nothing said during the primary season that he won't have to face in the general election, saying the president's re-election will be funded by "a billion dollars to go after me or whoever our nominee is."

"It's president Obama we need to be talking about," Romney said. "He has unveiled himself as a president that he's not the right person to lead this country."

And Gingrich said he "reserves the right to correct attacks against me," but agreed that the focus needs to be on the president: "Our only opponent is Barack Obama."

ABC's Arlette Saenz, Elicia Dover and Russell Goldman contributed reporting.