(Reuters) - Defense Secretary Leon Panetta defended the Obama administration´s decision not to arm the Syrian opposition, saying the country risked being pushed into an all-out civil war if efforts to secure a smooth political transition fail.

"We made a decision not to provide lethal assistance at this point. I know others have made their own decisions," Panetta said in an interview on Thursday.

"But I think it´s very important right now that everybody focus on a smooth and responsible political transition," he said.

"If we don´t get this done in a responsible way, there´s a real danger that the situation there could deteriorate into a terrible civil war."

The defense secretary also said the United States was concerned about the possibility that shoulder-fired anti-aircraft missiles, known as MANPADs, stolen from Libya last year during the fall of Muammar Gaddafi, could make their way to Syria. He cautioned, however, that he had seen no direct intelligence yet to confirm those fears.

Panetta also expressed confidence that Syria´s chemical weapons stockpiles were not at risk.

"We´re confident that these sites are being secured. And we see no evidence that any of them are in jeopardy of being violated," Panetta said.

The outside world is deeply divided in its response to an increasingly sectarian conflict in Syria that threatens to become a proxy war for regional powers. The United Nations estimates more than 10,000 people have been killed in 15 months of violence and unrest. Western diplomats say that month-old estimate is obsolete and the figure is likely much higher now.

Western nations and their Sunni Muslim allies in the Gulf and Turkey seek the overthrow of President Bashar al-Assad but are wary of direct intervention, while Russia, China and Shi´ite Iran - Assad´s strategic ally - have protected Assad from a tough international response.

Questions about weaponry being provided to Assad´s government came into focus last week when U.S. Secretary of State Hillary Clinton accused Russia of providing attack helicopters to Assad. Russia acknowledged on Thursday it was trying to send repaired combat helicopters to Syria aboard a vessel that apparently turned back after its insurance coverage was withdrawn.

Panetta said the U.S. hope was that "not only Russia, but other countries, don´t provide the kind of weapons and arms that result in killing more Syrians."

Pentagon spokesman Navy Captain John Kirby said Panetta was referring to the deaths of Syrian civilians by the Assad government and added he was not criticizing those countries that chose to arm the Syrian opposition.

EGYPT TRANSITION

On other Middle East crises, Panetta in the interview:

* Said Egypt´s military leaders still appeared broadly committed to a transition to civilian rule, but acknowledged his concern about new limitations on presidential powers that opponents equate with a coup.

"At least from the conversations I´ve had with them, I´ve gotten the impression that they want to continue to make this transition work," said Panetta, who spoke by phone last week with Field Marshal Hussein Tantawi, head of Egypt´s ruling Supreme Council of the Armed Forces, or SCAF.

Panetta said he was more troubled by the SCAF´s restrictions on presidential powers than by the decision of Egypt´s Supreme Court last week to dissolve the newly elected parliament.

"You have to respect the ruling of the court. So I understand that," he said. "The bigger concern is the announcement with regards to restricting powers."

* Played down the failure to secure a breakthrough at talks on Iran´s nuclear program this week, saying world leaders needed to keep the pressure on Tehran.

"My view right now is we keep pressing, keep doing everything we can to exhaust the diplomatic track, recognizing that the window is not unlimited in terms of remaining open," Panetta said.

Israeli leaders have suggested that country might attack Iran´s nuclear sites to prevent it from becoming a nuclear weapons power. (Editing by Warren Strobel and Peter Cooney) (© Thomson Reuters 2012. 06/22/12)