WASHINGTON — Former Sen. Rick Santorum has surged into a virtual tie in opinion polls with Republican presidential front-runner Mitt Romney, setting up a tough fight in the party's primary in Michigan on Feb 28.

Picking up support from voters aligned with the conservative Tea Party movement and white Christian evangelicals, Santorum rose rapidly to edge 2 percentage points ahead of Romney in a national poll released by the Pew Research Center on Monday.

Santorum, a social conservative, also came within 2 percentage points of Romney in a national Gallup poll, and was ahead by 15 percentage points in Michigan, where Romney was born and has been expected to do well.

“It's a real threat to the kind of sense of inevitability that Romney was trying to project a few short weeks ago,” said Christopher Arterton, a professor at George Washington University.

Almost twice as many Tea Party supporters and white evangelical Christians in the Pew poll chose Santorum over Romney, the former Massachusetts governor.

That survey had Santorum with 30 percent support from Republican and Republican-leaning voters, compared to 28 percent who preferred Romney.

The Gallup poll put Romney at 32 percent and Santorum at 30 percent. Former House of Representatives speaker Newt Gingrich, who led the field as recently as late January, was in third place with 16 percent.

The Public Policy Polling poll result in Michigan is probably most worrisome for Romney, whose father was governor of the state in the 1960s.

Santorum led Romney by 38 percent to 23 percent in the Midwestern state, which holds its primary in two weeks.