GOP presidential candidates former Massachusetts Governor Mitt Romney (L) and Texas Governor Rick Perry debate illegal immigration as they take part in the CNN Western Republican debate in Las Vegas, Nevada
GOP presidential candidates former Massachusetts Governor Mitt Romney (L) and Texas Governor Rick Perry debate illegal immigration / undocumented workers. Reuters

(Reuters) - Republican presidential candidates said on Saturday they would stop Iran from developing an atomic bomb but differed over how to do it in a debate that tested their knowledge of world hot spots.

The economy has been the No. 1 issue for the 2012 election campaign, so the CBS News/National Journal debate offered a rare opportunity to hear the candidates explain how they would handle the job as commander-in-chief.

The candidates made no major stumbles during the first hour of the 90-minute gathering, but Texas Governor Rick Perry's belief that the United States should consider eliminating foreign aid to Pakistan stirred debate among the candidates.

Newt Gingrich, who came to Spartanburg, South Carolina, riding a new wave of support as the conservative alternative to the more moderate Mitt Romney, declared he would launch covert operations within Iran in order to be able to deny them later.

Romney, who for months has been a front-runner to win the right to challenge President Barack Obama in the election next year, vowed in the debate at Wofford College to prevent Iran getting a nuclear weapon.

One thing you can know is if we elect Barack Obama, Iran will have a nuclear weakpon, said Romney, a former Massachusetts governor. If you elect me ... as the next president they will not have a nuclear weapon.

The U.N. nuclear watchdog, the International Atomic Energy Agency, on Tuesday reported that Iran appears to have worked on designing an atomic bomb and may still be conducting secret research related to building such weapons.

Businessman Herman Cain, who has been dogged by sexual harassment allegations recently, said the only way to stop Iran from developing a nuclear weapon was through economic means, squeezing Tehran through sanctions and boosting Iran's opposition movement.

Perry, hurt by a string of poor debate performances, including an embarrassing gaffe Wednesday night that some observers say might have crippled his campaign, was insistent that Washington should consider cutting aid to Pakistan.

While Gingrich agreed, Rick Santorum was adamantly opposed.

Pakistan is a nuclear power, Santorum said. We cannot be indecisive about whether Pakistan is our friend. They must be a friend.

None of the eight candidates on the stage have much in the way of foreign policy experience, save for former U.S. ambassador to China Jon Huntsman, but they all criticized Obama for mishandling U.S. relations abroad..

(Editing by Paul Simao)