Republican White House hopeful Newt Gingrich has surged ahead of rival Mitt Romney nationwide, but his lead in Iowa has faded ahead of the January 3 caucuses, two new polls showed. Gingrich, the former speaker of the House of Representatives, and Romney are seeking their party\'s nomination to take on Democratic President Barack Obama in the November 2012 election. The Iowa vote, which kicks off the Republican presidential nominating process, will be seen as a crucial test of strength for Gingrich, who only weeks ago took the lead from long-time frontrunner Romney. Gingrich now has 40 percent support among likely Republican voters nationwide, far ahead of the 23 percent support for Romney, a former governor of Massachusetts, according to a new Wall Street Journal/NBC News poll. National polls are not decisive in a contest fought on a state-by-state basis, but do reflect the temperature of national opinion of a particular candidate. In Iowa, Gingrich tops a Public Policy Polling survey of likely Republican voters with 22 percent support, just slightly ahead of Texas Congressman Ron Paul with 21 percent -- a major drop from the nine-point lead he enjoyed in the previous PPP survey one week ago. Romney\'s support in Iowa -- a largely rural midwestern state which barely figures in the general election but is key as the first official nominating contest -- was unchanged at 16 percent since last week. \"Newt Gingrich’s momentum is fading in Iowa,\" said PPP president Dean Debnam. Gingrich has come under fire from members of the party\'s religious base over his admitted extramarital affairs. Both Romney and Texas Governor Rick Perry have run ads in Iowa emphasizing their family values credentials. \"When it comes to his character record, he’s a very fine, empty suit with a broken zipper,\" wrote Iowa pastor Albert Calaway, a member of the Truth, Values and Leadership evangelical group, according to local media. Gingrich has also been criticized for accepting some $1.6 million as a consultant to Freddie Mac, the government-owned mortgage lender and target of conservative critics. \"The attacks on him appear to be taking a heavy toll,\" PPP said in a statement, noting that his support among the ultra-conservative Tea Party wing of the party has slipped from 35 percent to 24 percent. Gingrich has had difficulty forming a steady campaign organization to do battle against Romney\'s well-financed campaign juggernaut. A win in Iowa, where voters have traditionally been especially conservative, could sweep Gingrich to a strong showing in the New Hampshire primaries -- where Romney is favored to win -- on January 10. It could also give the former Georgia congressman significant momentum going into January primaries in the southern states of South Carolina and Florida, where he is expected to do well. As for Paul, PPP said he has strong support among young voters, independents and new voters in Iowa which could spell \"a big upset\" on January 3. Romney has failed to excite Republican voters, in part because of what is seen as \"flip-flopping\" on issues such as same-sex marriage and abortion. His Mormon faith also has sparked mistrust among conservative Christians, who form the party\'s backbone. In the national WSJ/NBC poll, Paul comes in third with nine percent, followed by congresswoman Michele Bachmann at eight percent and Texas Governor Rick Perry at six percent. PPP surveyed 555 likely Iowa Republican caucus voters between December 11-13. The poll has a plus or minus 4.2 point margin of error. The WSJ/NBC poll surveyed 1,000 adults between December 7-11 and has an overall plus-minus 3.1 percentage point margin of error.