Gingrich acknowledged that negative advertisements by political opponents had dented his popularity but suggested he would refrain from launching his own attacks while responding more aggressively to criticism of his record.
"I will be back on a positive basis, I will ... tell you what I stand for and I will answer any question that comes up based on the false and inaccurate advertising of some of my friends," Gingrich told a crowd of about 250 people at a campaign event.
A Public Policy Polling survey of likely participants in the January 3 Iowa caucuses -- the first-in-the-nation Republican nominating contest -- showed the former House speaker dropping to third place from first in the Midwestern state in the span of a week. Congressman Ron Paul of Texas led the new poll, which was released on Monday.
Gingrich's lead also evaporated in national polling as Republican candidates competed for the right to face President Barack Obama, a Democrat, in the November 2012 presidential election.
"Newt Gingrich's campaign is rapidly imploding and Gingrich has now seen a big drop in his Iowa standing two weeks in a row," Public Policy Polling, which is affiliated with the Democratic Party, said in a statement.
Gingrich earned just 14 percent support in the new Iowa poll compared to 22 percent a week ago and 27 percent two weeks ago.
Paul took over the lead in Iowa with 23 percent in the new polls, an increase of 5 percentage points over the past weeks. Former Massachusetts Governor Mitt Romney, who has been seen as Gingrich's main national rival, was second with 20 percent.
The survey of almost 600 people, taken December 16-18, had a 4 percentage point margin of error.
Another poll, by CNN/ORC International, showed that Gingrich and Romney were tied with 28 percent of support nationally from Republicans and Republican-leaning independents.
An onslaught of television and radio commercials by Gingrich's opponents that paint him as unreliable and a Washington insider has taken a toll.
"It's tough not to feel the effects in millions of dollars in advertising spent against you with no comparable response," said Tim Albrecht, spokesman for Republican Iowa Governor Terry Branstad and a former Romney staffer during Romney's unsuccessful run for the Republican presidential nomination in 2008.
Gingrich acknowledged that criticisms aimed at him by rivals -- omnipresent on Iowa television and radio -- had taken a toll.
"You get enough negative ads before you start answering them, your numbers go down for a while," he told reporters after speaking to a small crowd at Global Security Services, a small business.
'WORLD IS DANGEROUS'
He nevertheless took a swipe at his rival Paul, who has opposed much of U.S. military action abroad, while discussing concerns about North Korea's nuclear capabilities.
"The world is dangerous," he said. "I really stand apart from some of our candidates in believing we need a strong defense."
Gingrich's personal favorability numbers also fell during the past two weeks among Iowa voters polled ahead of the January 3 caucuses, the polling firm said.
Gingrich's front-runner status has prompted attacks from rivals who say he is an unreliable conservative and an influence peddler, particularly because of fees he earned from Freddie Mac, a mortgage giant tied to the economic recession.
"(Gingrich) is taking an unprecedented beating. ... I have just never seen so many negative, substantively negative ads aimed at one candidate from so many different angles," said Cary Covington, a professor of political science at the University of Iowa. "Ron Paul is just eviscerating Newt Gingrich in the ads."
Iowa political operatives said there is still plenty of time for more changes in the two weeks before the caucuses.
"Newt may have peaked at the right time or peaked just a little bit too early," said Will Rogers, one of the members of Gingrich's campaign team who resigned en masse in June amid frustration over how it was being run.
Rogers, who has returned to support Gingrich as a volunteer and is heavily involved with the Republican Party, said polls represent only a snapshot in time and said it seems that many Iowa voters still remain undecided.
Rogers said Paul was benefiting from his strong organization in Iowa, unlike Gingrich who had to scramble to beef up his staff as he rose in the polls.
"You don't know where Iowans truly sit until January 3," Albrecht said. "There's an unprecedented level of uncertainty this late."
"Caucuses always surprise people at the end. One thing caucuses do is defy conventional wisdom. Someone always dramatically outperforms poll numbers and someone under performs."
Gingrich has run an unorthodox campaign, signing books at events and talking about topics ranging from the economy to brain research and lunar mining.
"His campaign has been one of speeches and ideas, not one as organized as the others. And it's been interesting to watch at public forums and speeches that people have gravitated toward him and liked what he's had to say," said John Gilliland of the Iowa Association of Business and Industry.
"But it's hard when you're trying to build infrastructure when you're behind the eight ball," he said.
(Additional reporting by Paul Eckert and Lily Kuo in Washington; Writing by Deborah Charles; Editing by Will Dunham)
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