Evan Vucci, Associated Press
Presidential candidates Jon Huntsman Jr. and Newt Gingrich talk with Mitt Romney at a Republican presidential debate.

WASHINGTON — Mitt Romney's above-the-fray campaign style kept him atop the Republican presidential field for months, but it's raising concerns among his supporters now that Newt Gingrich has surged to challenge him.

Some Romney backers say their candidate must mix it up more aggressively, with Gingrich and with reporters, to prove he has the moxie to be the GOP challenger to President Barack Obama. Romney, the former Massachusetts governor, particularly caused concerns with his prickly responses in a recent Fox News interview. He needs to show more toughness and willingness to field questions, party insiders say.

The message seemed to resonate with his campaign Tuesday. Romney said he will appear on Fox News Sunday on Dec. 18, his first national Sunday talk show in nearly two years. He also fielded questions from reporters covering his Arizona visit, marking his third such "press availability" in four days.

The moves make sense to Rich Galen, a GOP strategist and former Gingrich aide who is neutral in the current race. "The lack of engagement strategy has served Romney pretty well," Galen said. "Now I think they've got to alter course and get him out there more."

Numerous Romney supporters had expressed concern over reports of him dodging reporters and in-depth questioning.

"It remains a mystery why Mitt Romney has done relatively few interviews," Jennifer Rubin, a conservative blogger for The Washington Post who often praises Romney, wrote on Monday. The much-discussed Nov. 29 Fox interview, she said, might have gone better "had it been one of dozens of TV interviews he'd given during the campaign. ... He's been the least interviewed candidate in the race."

In his 15-minute exchange with Fox News' Brett Baier, Romney bristled at questions about his changed views on abortion, climate change, immigration and gay rights, all of which are widely discussed in political circles.