Washington, Dec 15: A new poll finds Republicans don't believe former Massachusetts Gov. Mitt Romney's chief argument that his private-sector, outside-Washington background makes him a better presidential candidate than Newt Gingrich with his three decades in the capital.

The Associated Press-GfK poll released Wednesday also shows Romney has been unable to persuade Republicans he's more conservative than Gingrich, the former Speaker of the House of Representatives.

President Barack Obama's approval ratings are low and he remains vulnerable over his handling of the U.S. economy.

The poll showed that of all people surveyed, including Democrats and independents, Romney and the president are statistically even. Obama leads Gingrich 51 percent to 42 percent.

Romney and his aides know they have limited time to get voters' attention before the Jan. 3 Iowa caucus and the Jan. 10 New Hampshire primary.

In recent days, they have highlighted Gingrich's departures from conservative paths, subjected their own candidate to wider media scrutiny and emphasized the less-flattering aspects of Gingrich's Washington experience.

In essence, Romney is saying Gingrich has the wrong kind of Washington experience: cutting unwise deals with Democrats, letting power go to his head and cashing in on his name and contacts after leaving Congress.

The revised strategy is playing out in TV ads, in emails and in comments by Romney and his surrogates.

During a series of interviews while fundraising in New York, Romney told one media outlet that “zany is not what we need in a president” and another that Gingrich had “an extraordinary lack of understanding of how the economy works.”

To yet another, Romney mocked Gingrich's past accounts at a tony jeweler, saying: “He's a wealthy man — a very wealthy man.

If you have a half-a-million-dollar purchase from Tiffany's, you're not a middle-class American.”

Romney's campaign also rolled out an Internet video describing Gingrich as an unreliable conservative and using a clip of a climate change ad that the former House speaker filmed with House Democratic leader Nancy Pelosi.

Gingrich, in turn, sought to stay above the fray.

“They should run their campaign the way they want to and we're going to run our campaign the way we want to,” Gingrich told reporters after an event at the University of Iowa.

Romney aides say they will make greater use of the 2008 video in which Gingrich discussed climate change with Pelosi, who is villified by conservatives. They also are employing Republican officials who worked with Gingrich in the mid-1990s to argue that he was an erratic and unreliable leader during his four years as House speaker.

They hope the tactic might reverse the trend in polls that show Gingrich ahead of Romney, nationally and in early voting states.

The AP-GfK poll found Gingrich with an edge, but just within the margin of error.

But Romney has trouble proving his own conservative credentials.

During his time in Massachusetts, he supported legalized abortion, gun control and gay rights.

He changed those positions before his first bid for president, in 2008.

Romney says he was wrong not to sign Gingrich's 1994 Contract With America when he was running for a Senate seat.

Gingrich, 68, spent 20 years in the House, the last four as speaker after leading the Republican resurgence of 1994.

He left Congress in 1998 under an ethics cloud, following sharp clashes with Republican colleagues.

He then earned millions of dollars as a Washington-based consultant, speaker and writer.

Like Romney, Gingrich has changed positions on some issues, including how to address climate change.

Romney allies say their candidate is not panicking.

There is plenty of time for Gingrich to hurt himself through his propensity for hyperbolic and often boastful remarks, they say.

Also, the AP-GfK poll and other surveys of Republicans give Romney a clear edge on which contender has the best chance to beat President Barack Obama next year. Several advisers said Romney should let his friends or the news media make the “electability” argument for him, while he stays focused on Obama and the economy.

Romney's revised strategy calls for pointedly questioning Gingrich's conservatism and highlighting the seamier aspects of his time in Washington.

In doing so, Romney allies hope to provoke Gingrich into an outburst that will raise doubts about his stability or judgment.

Romney recently called on Gingrich to return the $1.6 million he made as a consultant to Freddie Mac, the quasi-government mortgage giant that many conservatives dislike.

Gingrich in turn said Romney should give back the millions he made as head of Bain Capital, a venture capital firm that sometimes laid off employees as it reorganized struggling businesses.

To Romney's delight, some conservative commentators questioned Gingrich's faith in capitalism.