Washington ? Defense Secretary Leon Panetta and the nation’s top military leader delivered a sober assessment Wednesday of Syria’s sophisticated air defenses and its extensive stockpile of chemical weapons in a strategic reality check to the demand for U.S. military action to end President Bashar Assad’s deadly crackdown on his people.

President Barack Obama’s 2008 rival, Republican Sen. John McCain, has called for the president to launch airstrikes against Assad to force him from power and end the bloodshed. The United Nations estimates that more than 7,500 Syrians have been killed, with hundreds more fleeing to neighboring nations to avoid the slaughter.

Army Gen. Martin Dempsey, the chairman of the Joint Chiefs of Staff, told the Senate Armed Services Committee that Obama has asked the Pentagon for a preliminary review of military options, such as enforcement of a no-fly zone and humanitarian airlifts. He insisted that the military would be ready if the commander-in-chief made the request.

“What are the potential missions, what is the enemy order of battle, what are the enemy’s capabilities or potential enemies? What are the troops we have available, and how much time. So, mission, enemy, terrain, troops and time. That’s a commander’s estimate,” Dempsey said of the initial step.

Panetta said they are waiting on Obama before doing more detailed contingency planning.

In Congress, only McCain’s closest Senate colleagues have echoed his plea. War-weary Republicans and Democrats have expressed serious reservations about U.S. military involvement in Syria after more than a decade of war in Iraq and Afghanistan, the divisive political fight last summer over U.S. intervention in Libya, and the possibility of an Israeli attack on Iran.

House Speaker John Boehner, R-Ohio, said this week that the situation in Syria is too muddled and military action would be premature, an opinion shared by many House Republicans who challenged Obama last year for dispatching the military to protect Libyans battling to overthrow Moammar Gadhafi. Republican presidential candidate Mitt Romney also said this week that he wasn’t prepared to support military action against Syria.

Panetta summed up the situation in stark terms.

“The fundamental issue that is before us is whether or not the United States will go in and act unilaterally in that part of the world and engage in another war in the Muslim world unilaterally. Or whether or not we will work with others in determining what action we take,” Panetta said.