By Andy Sullivan
WASHINGTON (Reuters) - Republican presidential candidate Mitt Romney on Sunday called for President Barack Obama to fire three top administration officials as he sought to harness voter anger over rising gas prices ahead of nominating contests in Puerto Rico and Illinois.
Top rival Rick Santorum, meanwhile, promised a crackdown on pornography and stood by comments he made earlier in the week that predominantly Spanish-speaking Puerto Rico should make English its official language if it wants to achieve statehood.
Romney, the Republican frontrunner, is fending off a growing challenge from Santorum in Illinois, which holds its primary contest on Tuesday in the state-by-state battle to determine who will face Democratic President Barack Obama in the November 6 election.
Fewer delegates are at stake in Puerto Rico's nominating contest on Sunday.
A bitter, drawn-out battle could compromise the eventual nominee's ability to take on Obama in the fall.
Republican candidates have seized on rising gasoline prices to argue that Obama's environmental efforts are hurting ordinary Americans who are struggling to recover from the deepest recession since the 1930s.
Gas prices have increased 53 cents since the start of the year to an average of $3.88 a gallon.
"When he ran for office he said he wanted to see gasoline prices go up," Romney said on Fox News Sunday.
Romney said Obama should fire the three top officials who oversee energy and environmental matters - Energy Secretary Stephen Chu, Interior Secretary Ken Salazar and Environmental Protection Agency Administrator Lisa Jackson.
"This gas-hike trio has been doing the job over the last three and a half years and gas prices are up. The right course is they ought to be fired," the former Massachusetts governor said.
Energy experts say that the price of gasoline is largely set by global markets, not government policies, and Obama has accused Republicans of pandering on the issue. Still, Obama and British Prime Minister David Cameron have discussed releasing strategic oil reserves to ease gas prices.
Santorum, whose opposition to gay marriage and birth control and positions on other hot-button social issues has won him a loyal following among Christian conservatives, said he would enforce anti-pornography laws that the Obama administration has ignored.
"They have not put a priority on prosecuting these cases. And in doing so they are exposing children to a tremendous amount of harm," the former U.S. senator from Pennsylvania said on CNN.
Santorum also defended his comments earlier in the week in which he said, incorrectly, that Puerto Rico would have to make English its official language in order to achieve statehood.
He accused Romney of hypocrisy for backing a resolution that would make English the official language of the United States while telling Puerto Ricans they would not face such a requirement.
"He's willing to say whatever he needs to say in order to get those votes. And I'm hopeful the people of Puerto Rico will see through the charade," he said.
Romney said Santorum's underfunded, poorly organized campaign would not be able to defeat Obama in the fall.
"This is not about a shoestring operation, this is about an operation that can be competitive with the president of the United States and beat him," he said.
(Additional reporting by Bill Trott; Editing by Paul Simao)