By Jason McLure
LITTLETON, New Hampshire (Reuters) - Presidential hopeful Newt Gingrich is ramping up his campaign in the key early primary state of New Hampshire in an attempt to undercut a stronghold of Republican rival Mitt Romney.
Gingrich, the former U.S. House speaker, has picked up two top New Hampshire operatives from Herman Cain's suspended campaign and now has 15 paid staff in the state.
He will soon open a fifth field office in a network that stretches from Littleton in the state's mountainous north to Salem, just over the border with Massachusetts, said Matthew LeDuc, a New Hampshire spokesman for Gingrich.
That compares with nine staff and one paid adviser for Romney, who has just one office in Manchester, the state's largest city, according to Romney spokesman Ryan Williams.
"We're definitely not ceding it," LeDuc said of the state that will hold the first primary of the 2012 presidential contest on January 10.
Romney, who has a vacation home in New Hampshire and is a former governor of neighboring Massachusetts, still leads in the state and has endorsements from most of its Republican powerbrokers. He rallied hundreds of volunteers last weekend to campaign on his behalf.
A CNN/Time poll taken November 29 to December 6 gave Romney 35 percent to Gingrich's 26 percent, with Texas Congressman Ron Paul third with 17 percent. The survey of 507 likely voters had a margin of error of plus or minus 4.5 percentage points.
As recently as a few weeks ago, most polls showed Romney leading by 20 to 25 points over various Republican rivals.
Seeking to quell Gingrich's momentum, Romney's campaign has bought television time in the state for a new advertisement in which the candidate highlights his stable family life.
In the ad, Romney describes himself as a "man of steadiness and constancy" who has been married to the same woman for 42 years and belonged to the same church his entire life.
Gingrich is on his third marriage, and left the Southern Baptists in 2009 to become a Roman Catholic.
On Thursday, Romney's campaign had a conference call in which former New Hampshire Governor John Sununu attacked Gingrich over his criticism of a plan floated earlier this year by Representative Paul Ryan to reform Medicare.
"I don't think Newt Gingrich cares about conservative principles," Sununu, who was also chief of staff under President George H.W. Bush, said in an interview on MSNBC. "Newt Gingrich cares about Newt Gingrich."
(Reporting by Jason McLure, editing by Ros Krasny and Cynthia Johnston)