The former Pennsylvania senator is preferred by 25 percent of the state's registered Republicans, a turn-around that has come partly at the expense of former House Speaker Newt Gingrich, whose support in the state has plunged.

Santorum was supported by just 2 percent of California GOP voters in a Field Poll taken last November. His growing popularity since then has been driven in part by those who said they identify with the tea party or classify themselves as strongly conservative.

Former Massachusetts Gov. Mitt Romney remained Republicans' top choice, getting support from 31 percent.

The survey's timing was key. Field interviewed Republicans Feb. 2-18, a period that included Santorum victories in Missouri, Minnesota and Colorado.