One option DOD leaders are pursuing is increasing U.S. military involvement in Jordan, sending an Army unit to Amman last week to help the country's military defend its shared border with Syria.
U.S. forces will also aid Jordanian military units "to identify and secure chemical weapons assets" that may make their way across the border, he added.
Earlier this month, Pentagon officials denied claims that U.S. military advisers in Jordan were secretly training anti-Assad rebels in clandestine camps in the country.
Aside from Jordan, Hagel said military planners are also preparing military options for "additional new contingencies" in Syria should the war bleed over into other countries like Turkey and Iraq.
Secretary of State John Kerry will visit Turkey and other nations in the region this week, he told members of the House Foreign Relations committee on Wednesday.
Hagel's comments come as congressional pressure on the Obama administration to provide military support for the rebels batting to oust longtime Syrian president Bashar Assad has ramped up significantly.
Committee chief Carl Levin (D-Mich.) is one of several Democrats who have begun to break ranks with Obama, calling for U.S. military and intelligence officials to take action in Syria.
"I believe the time has come for the United States to intensify the military pressure on Assad," Levin said during Wednesday's hearing.
That action, backed by Senate Republicans John McCain (R-Ariz) and Lindsey Graham (R-S.C.), include creating a no-fly zone on the Turkey-Syria border, sending U.S. warplanes to Syria to take out Assad's heavy weapons and directly arming the Syrian rebels.
Syria is "becoming more and more an impossible threat" to stability and security in the country and the region as a whole, McCain said.
"Any or all of these actions would send a critical message to Assad that it is time for him to go," Levin added.
Former Defense Secretary Leon Panetta told Congress earlier this year that the Pentagon supported arming the Syrian opposition, despite concerns about al Qaeda influence in the country, but was overruled by the White House.
Pentagon and U.S. intelligence officials have been wary of infiltration of anti-Assad forces by Islamic radicalists like al Qaeda and other militant groups since the early days of the uprising.
Those concerns have been the major roadblock in possible U.S.-led efforts to provide small arms and heavy weaponry to anti-Assad forces, due to fears those weapons could end up in the hands of al Qaeda fighters.
McCain hammered that decision, saying he has never seen a situation where national secuirty officials called for a course of action in Syria and elsewhere "and be overruled by someone in the White House."
Despite the Pentagon's war planning, the White House remains committed to finding a diplomatic solution to end the bloody Syrian civil war, which has now entered its third year.
Hagel backed the administration's stance in Syria during Wednesday's hearing.
"We have an obligation and responsibility to think through the consequences of direct U.S. military action in Syria," Hagel said. "Military intervention is always an option, but an option of last resort."
U.S.-led military operations could derail ongoing humanitarian and international aid efforts in the country, Hagel noted.
"Unilateral military action could strain other key international partnerships," since Washington has yet generate any real international support for armed intervention, Hagel added.
Should the U.S. go it alone in Syria, military action "could have the unintended consequence of bringing the United States into a broader regional conflict or proxy war," just as American forces are winding down the conflict in Afghanistan.
"The best outcome for Syria" is a peaceful, post-Assad transition to democracy, the Pentagon chief added.