WASHINGTON — With the Iowa caucus nearing and Newt Gingrich surging, Mitt Romney’s campaign strategies appear to be flagging in the Republican presidential race. He’s starting to adjust.

A new Associated Press-GfK poll finds that Republicans aren’t buying Romney’s chief argument: that his private-sector, outside-Washington background makes him a better candidate than does Gingrich’s three decades in the capital. Romney, the former Massachusetts governor, also has been unable to persuade Republicans he’s more conservative than Gingrich.

Romney and his aides are beginning to revamp. They 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, Romney’s campaign has 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.

For instance, Romney aides say they will make greater use of a 2008 video in which Gingrich appeared with then-Speaker Nancy Pelosi, D-Calif., to discuss climate change. They also are employing GOP 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.

“Gingrich is not nearly the conservative that everybody thinks he is,” said Mike

McKenna, a Republican lobbyist and strategist unaffiliated with the presidential campaigns.

“He is surging because some chunk of the electorate sees him as the authentic conservative in the race. Romney doesn’t need to prove he’s the authentic conservative. He just has to cast doubt on whether it’s Gingrich.”

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.