WASHINGTON — Former House speaker Newt Gingrich's commanding lead among Republican presidential hopefuls in Iowa has eroded dramatically in the past week, a poll in the key state out Tuesday shows.

Gingrich tops the survey with 22 percent support, just slightly ahead of Congressman Ron Paul who has 21 percent, according to the Public Policy Polling survey of likely Republican voters ahead of the January 3 caucuses, which kick off the 2012 presidential nominating season.

Gingrich, who is seeking the Republican nomination to take on President Barack Obama in the November 2012 election, enjoyed a nine-point lead in the previous Iowa PPP survey December 3-5.

Former Massachusetts governor Mitt Romney, once seemed like the inevitable nominee, has 16 percent support in Iowa, unchanged since the previous PPP survey.

"Newt Gingrich's momentum is fading in Iowa," said Public Policy Polling president Dean Debnam.

The attacks against Gingrich "appear to be taking a heavy toll," the pollsters said, noting that his support among the ultra-conservative Tea Party wing of the party has slipped from 35 percent to 24 percent.

The ex-speaker is ahead among party faithful in national polls, a lead that lead may mean little if he does not win in Iowa. An Iowa win could sweep him to victory in the New Hampshire primaries on January 10, and give him significant momentum going into January primaries in the southern states of South Carolina and Florida.

Yet it is Ron Paul who is now surging as the "other-than-Romney" Republican candidate.

According to the pollster Paul has strong support among young voters -- voters who historically show much enthusiasm but cast ballots in lower numbers than older voters.

It is unclear if Gingrich will suffer the same fate as Congresswoman Michele Bachmann, businessman Herman Cain -- who dropped out of the race amid a growing sex scandal -- and Texas Governor Rick Perry, all of whom briefly led popularity surveys among Republicans at different times as an alternative to Romney.

Bachmann has seen her support slip from 13 percent to 11 percent in the Iowa poll, while Perry has been stuck at nine percent support.

PPP surveyed 555 likely Republican caucus voters between December 11-13. The poll has a plus or minus 4.2 point margin of error.