By David Alexander
WASHINGTON (Reuters) - Defense Secretary Leon Panetta on Wednesday defended caution in trying to end the violence in Syria, despite biting criticism from lawmakers who questioned how many people would have to die before the Obama administration used force.
Even as Panetta and General Martin Dempsey, chairman of the Joint Chiefs of Staff, emphasized the need for international consensus on Syria and the challenge of any military action, they told a Senate panel that very preliminary military planning was under way.
They said that at President Barack Obama's request, the Pentagon had studied U.S. military options in Syria, assessing issues like potential missions and Syria's troop line-up.
Panetta said the Pentagon had discussed the findings with the National Security Council and was working through further ideas related to those options. But the department was "waiting for the direction of the president" before beginning more detailed contingency planning, he said.
Obama has shown no enthusiasm for U.S. participation in an election-year military mission to unseat Syrian President Bashar al-Assad. He said on Tuesday it was a mistake to think there was a simple solution the yearlong crackdown on the Syrian opposition or that the United States could act unilaterally.
Dempsey underscored the basic nature of the planning.
"The commander's estimate process really looks at ... what are the potential missions, what is the enemy order of battle, what are the enemy's capabilities ... what are the troops available and how much time. So mission, enemy, terrain, troops and time. That's a commander's estimate," he told the Senate Armed Services Committee.
Panetta and Dempsey told the panel that U.S. intelligence agencies believed it was just a matter of time before Assad was ousted from power.
"Their view is that the state of this insurgency is so deep right now ... that ultimately he will fall one way or another," Panetta said. But some senators questioned if the administration was using that assessment to justify its slow response.
"How many additional civilian lives would have to be lost in order to convince you that the military measures of this kind that we are proposing are necessary to end the killing?" asked Republican Senator John McCain, who has urged air strikes on Syria.
Obama has urged Assad to halt the violence against his people and step aside to allow a democratic transition. But efforts to develop an international consensus toward Syria have met resistance.
Russia and China have opposed any intervention similar to the one last year in Libya and last month vetoed a U.N. Security Council resolution backing an Arab League call for a political transition that would have Assad cede power.
The United Nations estimates 7,500 people have been killed in Syria since unrest swept the Arab world last year and protesters began calling for Assad to step aside and allow free elections. Syria said in December that government opponents had killed some 2,000 member of the security forces.
Panetta told the committee the administration was still trying to forge a consensus on addressing the violence in Syria.
"That makes the most sense. What doesn't make sense is to take unilateral action at this point," Panetta said.
Aram Nerguizian, an analyst at the Center for Strategic and International Studies, said defense officials were justified in taking a cautious approach toward Syria due to its capable military and its political and sectarian divisions.
"The reality is that Syria is just too big and too complex to jump into this without taking a real pulse of who the players are, what the real contingencies are and how this can play out in real-world terms," Nerguizian said.
Some lawmakers pressed for the use of U.S. air power to strike at Syrian tanks and artillery that have been used to besiege opposition cities. Air power was used similarly in Libya last year as well as in Bosnia and Kosovo in the 1990s.
But Dempsey warned that Syrian air defenses were significantly more advanced than those of Libya or Bosnia.
"They have approximately five times more sophisticated air defense systems than existed in Libya covering one-fifth of the terrain," Dempsey said. "All of their air defenses are arrayed on their western border, which is their population center."
Dempsey expressed reluctance to discuss in a public forum which countries were supplying weapons to Syria. But he acknowledged Iran was sending small-caliber arms, rocket-propelled grenades and anti-tank weapons to Assad's forces. Other countries with foreign sales agreements with Tehran were providing "upper-tier stuff, including air defenses," he said.
As senators prodded the Obama administration for action toward Damascus, a panel in the U.S. House of Representatives voted on Wednesday for a measure to impose sanctions on Syria's energy sector and for referring Assad to a war crimes tribunal.
(Additional reporting by Andrew Quinn and Susan Cornwell; Editing by Peter Cooney)