WASHINGTON (CNN) -- America is working to remove al-Assad's regime in Syria through diplomatic pressure, Secretary of Defense Leon Panetta said Wednesday, but he warned against U.S. military intervention.
"For us to act unilaterally would be a mistake," Panetta said in his opening statement to the Senate Armed Services Committee hearing on Syria. He noted there is no consensus among nations for intervention.
Panetta said military options are being considered, but he asked the senators to “recognize the limitation of military force, especially U.S. boots on the ground."
Sen. John McCain, the highest-ranking Republican on the Armed Services Committee continued his impassioned crusade to get the U.S. military to use force to help the opposition fighters trying to overthrow Syrian dictator Bashar al-Assad. McCain said Wednesday that intervening and pushing out al-Assad would be "a geopolitical success of the first order."
"The United States has a clear national security interest in stopping the slaughter in Syria and forcing Assad to leave power. The end of the Assad regime could sever Hezbollah's lifeline to Iran, eliminate a longstanding threat to Israel, bolster Lebanon's sovereignty and independence, and remove a committed state sponsor of terrorism that has engaged in the proliferation of weapons of mass destruction," McCain said.
"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," McCain asked Panetta. "How many more have to die? Ten thousand more? Twenty thousand more? How many more?"
Panetta responded that the United States is working to build an international consensus for action.
"What doesn't make sense it is to take unilateral action at this point," he said with equal emotion. "Before I recommend that we put our sons and daughters in uniform in harm's way, I have got to make very sure that we know what the mission is. I've got to make very sure we know whether we can achieve that mission, at what price and whether it will make matters better or worse."
The increase in pressure on the Pentagon to use force in Syria began Monday when McCain, a former Navy fighter pilot, called for the Department of Defense to begin air strikes in Syria.
Wednesday, for the first time, Defense Department leaders spelled out what military options the United States might use should diplomatic and economic pressure fail to end al-Assad's crackdown.
Those options, said Gen. Martin Dempsey, chairman of the Joint Chiefs of Staff, "include humanitarian relief, (a) no-fly zone, maritime interdiction,(a) humanitarian corridor and limited aerial strikes, for example."
Dempsey revealed that the White House has asked the military to provide the president with a military plan.
"The president of the United States through the National Security Staff has asked us to begin ... the estimate of the situation," Dempsey said. That estimate, he explained, will include looking at potential missions, the capabilities of the enemy, and U.S. military assets that are available.
The military has discussed those options with the president and his national security staff, Panetta said. Dempsey said he is confident the United States could carry out military missions in Syria.
"We're extraordinarily capable. And we can do just about anything we're asked to do," he said. But he made clear that Syria will not be a repeat of the recent operations in Libya.
"They have approximately five times more sophisticated air defense systems than existed in Libya covering one-fifth of the terrain," he said. "All of their defenses are arrayed on their western border, which is their population center. So five times the air defense of Libya, covering one-fifth of the terrain."
Dempsey and Panetta raised the concern that U.S. military action could make matters inside Syria and the entire region worse.
"There is every possibility of a civil war, and a direct outside intervention in these conditions not only would not prevent that, but could make it worse," Panetta said.
One problem is Syria's substantial chemical and biological weapons stockpile. Dempsey said the stockpile is on a magnitude of "a hundred times more than we experienced in Libya."
But Panetta returned again to the issue of international support for use of force in Syria.
"There is no simple solution here," he said. "The reasons for the differences between our approach with Libya and the current approach to Syria are clear.
Although there has been widespread support in the Security Council and the Arab League for military intervention in Libya, no such consensus currently exists with regards to Syria. For us to act unilaterally would be a mistake."
That issue got Panetta in a tight spot when he was being questioned by Sen. Jeff Sessions, R-Alabama.
"We spend our time," Sessions said, "worrying about the U.N., the Arab League, NATO, and too little time, in my opinion, worrying about the elected representatives of the United States. As you go forward, will you consult with the United States Congress?"
Panetta replied, "You know, again, our goal would be to seek international permission. And we would come to the Congress and inform you and determine how best to approach this."
Sessions latched on to Panetta's use of the word "permission," saying, "Well, I'm troubled by that. I think that it does weaken the ability of the United States to lead."
He went on to say, "I do think, ultimately, you need the legal authority from the United States of America, not from any other extra-territorial group that might assemble."
Sen. Carl Levin, the chairman of the committee, tried to help out Panetta: "If you're seeking international coalition, having that kind of international legal basis will help. I think that's what you're trying to say."
"That's what I am trying to say," Panetta responded.
McCain has made an issue of those who urge caution in Syria because the United States might end up helping opposition groups who are not friendly to the America.
"I reject the argument that we, quote, 'don't know who they are,'" he said. "We spend a lot of money on defense and we spend a lot of money on intelligence.
We should know who these people are. And it would be easy enough to find out."
But Dempsey said it is not that simple, noting there are "approximately 100 groups that we have identified as part of the opposition."
"We are not suggesting that part of al Qaeda that has made its way to Syria, has aligned itself or is in bed with the opposition," the general said. "But they are there to exploit it. And that is a factor that we have to consider."