A poll by the Pew Research Center in Washington gave Santorum 30 percent of the vote among those surveyed Feb. 8-12 to 28 percent for Romney. Newt Gingrich received 17 percent and Ron Paul 12 percent. As recently as a month ago, the Pew poll had found Romney leading Santorum 31 percent to 14 percent.
Gallup pollsters in Princeton, N.J., gave Romney 32 percent and Santorum 30 percent among the registered Republican voters they surveyed Feb. 8-12. Gingrich, who had led the field as recently as late January, polled 16 percent and Paul was at 8 percent.
Santorum's Gallup numbers were up from 16 percent just days earlier.
The Pew poll found Democratic President Barack Obama with a 10 percentage-point lead over Santorum, an 8-point margin over Romney and an 18-point lead on Newt Gingrich in general election match-ups.
The Pew poll surveyed 1,501 adults. The margin of error was not provided.
The Gallup results from 1,162 respondents carry a plus or minus 4 percentage-point margin of error.