Acknowledging he is working to fend off a surging Newt Gingrich, presidential candidate Mitt Romney on Friday tried to change the subject from his unreleased tax returns to the ethics investigation the former House speaker faced 15 years ago.

When asked if Gingrich should release the Ethics Committee report that resulted in a rare reprimand for a House speaker, Romney replied, "Of course he should."

Romney said: "Nancy Pelosi has the full record of that ethics investigation. You know it's going to get out ahead of the general election."

In fact, the 1,280-page committee report on Gingrich is already public. Campaign officials said Romney was referring to other documents that Gingrich has referred to and that Pelosi has also mentioned.

"Given Speaker Gingrich's newfound interest in disclosure and transparency, and his concern about an `October surprise,' he should authorize the release of the complete record of the ethics proceedings against him," Romney spokeswoman Gail Gitcho said.

In December, Pelosi told Talking Points Memo that she had served on the committee that conducted the investigation and implied that more information about the investigation could come to light. At the time Gingrich said the House should retaliate against Pelosi if she released any additional information.

"We turned over 1 million pages of material," Gingrich said then. "We had a huge report."

Gingrich's campaign said Romney's criticism represented a "panic attack" on the part of his campaign.

Romney on Friday said again that he wouldn't release his tax returns until April, which would probably be after Republicans choose their nominee.

Romney's campaign is visibly rattled, given that his standing in polls has slid after a week of constant attack ads and self-made problems. He came to South Carolina after twin wins in Iowa and New Hampshire, only to see his Iowa victory thrown into question because of problems with the count. He's also spent a week trying to answer questions about his personal wealth and when he will release his tax returns.

"I realize that I had a lot of ground to make up and Speaker Gingrich is from a neighboring state, well-known, popular in the state," Romney said as he campaigned in Gilbert. "Frankly, to be in a neck-and-neck race at this last moment is kind of exciting."

Romney's campaign has rolled out endorsement after endorsement this week as he has tried to build a case that he is the most electable nominee. Ohio Sen. Rob Portman joined him on Thursday and Virginia Gov. Bob McDonnell campaigned with him Friday.

But the campaign's attack message has jumped from rival to rival and topic to topic as he's fought to stay afloat here.

At the beginning of the week, Romney was attacking rival Rick Santorum over voting rights for felons. Then he went after Gingrich's claims that he created jobs under President Ronald Reagan, saying Gingrich was living in "fantasyland." Meanwhile, his surrogates held a series of conference calls attacking his rivals.

In Thursday night's GOP debate, Romney continued his string of off-message remarks about his wealth, saying he has lived "in the real streets of America." A multimillionaire, he has three homes, one each in Massachusetts, California and New Hampshire.