At a roundtable discussion in Monroe, Romney also was careful to praise unions, citing the carpenters' union for helping workers improve their skills. "But I believe union and non-union shops should compete on a level playing field" for government contracts, Romney said.
Romney pollster Neil Newhouse said his candidate's early showing with the working class has been "a soft spot" because Santorum and Gingrich have targeted those same voters. That won't translate to Election Day, Newhouse said.
"The general election will be about President Obama and his accomplishments and lack thereof," Newhouse said.
Combined figures for the first five states to vote — Iowa, New Hampshire, South Carolina, Florida and Nevada — show ideology was also a factor. Just 22 percent of Romney's votes came from working-class whites who consider themselves very conservative. Santorum got 52 percent of his votes from that group and former House Speaker Newt Gingrich, Romney's biggest rival at the time, got 45 percent.
In those early contests, Romney led Gingrich by 43 percent to 28 percent among whites who completed college, the polls show.
That gap shrank to a 39 percent-to-33 percent Romney advantage among whites without college degrees. White men who haven't graduated college tilted 37 percent to 33 percent toward Gingrich.
Romney's 20-percentage-point advantage over Gingrich among white female college graduates in those states falls slightly, to 15 points, among less educated white women.
Santorum swept GOP presidential contests in Colorado, Minnesota and Missouri last week. There were no exit polls in those races, but the combined surveys for the first five states show Santorum, who had not yet built momentum as a candidate, trailing both Romney and Gingrich badly among white working-class voters.
Ironically, Romney's problem echoes an even more serious weakness that candidate Barack Obama showed in 2008 when trying to reach those same working-class white voters.
Obama lost them badly in the Democratic primaries to rival Hillary Rodham Clinton before losing them by 18 percentage points to GOP candidate Sen. John McCain that November. Obama remedied that by coming close among white college graduates and prevailing overwhelmingly among minorities.
Republicans want to drive their margin among working-class whites as high as possible this year to offset Obama's advantage with minorities. Working-class whites comprise around 4 in 10 voters in recent general elections.
Obama campaign spokesman Ben LaBolt says Romney will be hurt among these voters by his background at Bain, the private equity firm, whose corporate buyouts sometimes eliminated jobs.
"The essential question of the election is, 'Who's going to restore economic security for the middle class?'" LaBolt said.
The data is based on surveys conducted for The Associated Press and the television networks by Edison Research as voters arrived at or left randomly selected sites in this year's GOP caucuses and primaries in Iowa, New Hampshire, South Carolina, Florida and Nevada. The results of the five surveys were combined and each was weighted to reflect its share of the votes cast.
The combined survey involved interviews with 11,376 voters and had a margin of sampling error of plus or minus 1 percentage point.
AP Deputy Director of Polling Jennifer Agiesta and Associated Press writers Charles Babington, Philip Elliott and Steve Peoples contributed to this report.
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