The top U.S. military commander in Europe said Tuesday that NATO forces are preparing contingency plans for operations in Syria if called upon to do so by the United Nations.

“We are looking at a wide range of operations, and we are prepared — if called upon — to be engaged as we were in Libya,” Adm. James G. Stavridis, told the Senate Armed Services Committee as the war in Syria entered its third year. NATO forces led the military effort last year that toppled Libyan strongman Muammar el-Qaddafi.

In reply to a question by Arizona Republican John McCain, Stavridis said one of the options under consideration would break the stalemate on the ground between forces loyal to Syrian President Bashar al-Assad and insurgent forces and drive Assad from power.

McCain is an outspoken supporter of U.S. military action against Assad — a position that has few supporters among his colleagues on Capitol Hill or in the White House.

NATO military action would require a U.N. Security Council resolution, along with the agreement of the alliance’s 28 members. But with the United States weary from more than a decade of war in Iraq and Afghanistan, President Barack Obama has opposed American military operation in Syria.

His administration has provided around $385 million so far in humanitarian aid for Syria and refugee assistance through the United Nations, local Syrian organizations and neutral aid organizations such as the International Committee of the Red Cross, which are required to work through host governments. As a result, about 40 percent of that aid has gone to areas controlled by the Syrian regime, according to Deborah L. Sisbarro, a spokeswoman for the State Department’s Bureau of Population, Refugees, and Migration.

At another hearing, U.S. and international aid officials painted a grim picture of the humanitarian crisis in Syria and neighboring countries. In addition to more than 70,000 people killed so far, the officials said thousands of Syrians were fleeing daily to Iraq, Jordan, Lebanon and Turkey, which could have as many as 1 million Syrian refugees each by the end of the year.

“The humanitarian situation is beyond description,” Antonio Guterres, the United Nations High Commissioner for Refugees, told the Senate Foreign Relations Middle East subcommittee. Guterres leads the effort to establish camps for the refugees, but he said he faced a severe shortage of funds to care for that many people.

Just before the Senate hearing, Pennsylvania Democrat Bob Casey, who chairs the Middle East panel, and Florida Republican Marco Rubio said they planned to introduce a bill that would provide humanitarian and non-lethal military aid, such as body armor and communications equipment, directly to Syrian opposition groups that have been thoroughly vetted. The precautions are to prevent such equipment from falling into the hands of Islamic extremists fighting the Assad regime.

But the two lawmakers left open the possibility of offering further legislation that would authorize arming the rebels.

“Down the road we may make another determination,” Casey said at a news conference.