The Republican presidential hopefuls meet on Tuesday for their second foreign policy debate in 10 days, with Newt Gingrich looking to extend a campaign surge that has propelled him to a lead over Mitt Romney in polls for the 2012 race.

The debate will shine a spotlight on Republican differences over Iran, Pakistan, the use of waterboarding, and foreign aid in a race that so far has focused largely on economic issues and featured few policy clashes among the top contenders.

Gingrich, Romney and six other Republicans take part in the 8 p.m. debate at Washington's DAR Constitution Hall, which airs live on CNN.

Gingrich could have the most to lose in Tuesday's showdown. He is the latest in a series of conservatives to challenge the more moderate Romney for the top spot in the Republican race for the right to face Democratic President Barack Obama in 2012.

A CNN/Opinion Research poll on Monday showed Gingrich, a former speaker of the U.S. House of Representatives, with a 4-point national edge over Romney, the former Massachusetts governor who has hovered near the top of polls all year.

Conservatives have failed to coalesce around a clear alternative to Romney, but Gingrich's campaign has soared in recent weeks as rivals like businessman Herman Cain and Texas Governor Rick Perry faltered in the spotlight.

The debate, the 11th of the year for the Republican candidates, comes barely more than a month before Iowa kicks off the state-by-state nominating fight. But the focus on foreign policy, which has taken a backseat to the economy, could limit its long-term impact.

"There are differences in views among the Republican presidential candidates on foreign policy, but that isn't where the interest has been for voters or the media," Republican strategist Matt Mackowiak said.

FOREIGN POLICY DIFFERENCES

Those differences were in full view at the last debate in South Carolina on November 12, when candidates spelled out differing views on using military force to halt Iran's nuclear ambitions, a timetable for withdrawal of U.S. forces in Afghanistan, and the use of waterboarding in interrogations.

Romney forcefully supported a military option if needed to stop Iran's nuclear development, and Gingrich said he would back "whatever steps are necessary" and proposed a covert campaign against Iran's scientists. Cain and U.S. Representative Ron Paul opposed military action.

On Pakistan, Perry said he would look at whether to eliminate U.S. aid to Pakistan, a move Gingrich supported. But Rick Santorum, a former U.S. senator, said Pakistan's nuclear weapons made it imperative that it remain a U.S. friend.

Romney, Cain and Representative Michele Bachmann backed the renewed use of waterboarding for terrorism suspects, while Paul and former Utah Governor Jon Huntsman opposed it. Waterboarding is a simulated drowning technique that critics call torture.

Huntsman, the former U.S. ambassador to China, is the only one of the Republican contenders with any foreign policy experience. Democrats have criticized the Republican field for a lack of substance in the subject.

Cain, whose campaign has faded after a series of sexual harassment allegations that he denied, is also likely to face new questions at the debate about his foreign policy expertise after a much-publicized gaffe on Libya last week.

The former pizza executive was stumped when asked by a Wisconsin newspaper editorial board about Obama's policy in Libya.

"OK, Libya," Cain said, stalling for time and staring at the ceiling as he searched for an answer. "I gotta go back, see, got all this stuff twirling around in my head," he said.

The debate, co-sponsored by the Heritage Foundation and American Enterprise Institute, is the first presidential debate in Washington since a 1960 face-off between Democrat John Kennedy and Republican Richard Nixon that helped launch Kennedy's run to the White House.