Until Thursday, the Pentagon had only said publicly that U.S. policy is to give only humanitarian assistance to rebels battling President Bashar Assad's regime. Providing arms has been the subject of ongoing internal administration debate.
Defense Secretary Leon Panetta said President Barack Obama made the final decision against arming the rebels.
"Obviously there were a number of factors that were involved here that ultimately led to the president's decision to make it nonlethal," Panetta said. "I supported his decision in the end."
Gen. Martin Dempsey, chairman of the Joint Chiefs of Staff, also acknowledged the Pentagon endorsement of the idea, telling Sen. John McCain, R-Ariz., "We did."
McCain, in a statement released later, said it was unfortunate that their advice was not heeded by the president.
"The crisis in Syria represents a graphic failure of American leadership," McCain said. "I urge the president to heed the advice of his former and current national security leaders and immediately take the necessary steps, along with our friends and allies, that could hasten the end of the conflict in Syria."
At the State Department, spokeswoman Victoria Nuland declined to discuss internal policy decisions.
But, in the past administration officials have made it clear there have been differing views on suggestions that the U.S. provide arms to the rebels.
"Arms are not a strategy; arms are a tactic," the U.S. ambassador to Syria, Robert Ford told a conference in Washington late last year. "A military solution is not the best way for Syria. Efforts to win this by conquering one side or the other will simply prolong the violence and actually aggravate an already terrible humanitarian situation. Syria needs a political situation."
The administration has expressed concern about the difficulty of determining which opposition groups are tied to al-Qaida-insurgents who might get U.S.-supplied arms. But some have urged the U.S. to supply weapons to opposition groups in order to hasten Assad's departure and prevent rebels from taking weapons from terror-linked groups.
After 22 months and more than 60,000 dead, Syria's crisis appears to have reached a stalemate, with neither side making significant battlefield gains likely to bring about a military victory any time soon.
The U.S. government has provided about $210 million in humanitarian assistance to Syrians in the country as well as refugees, including food, medical aid, blankets and winter supplies.
Associated Press writer Sagar Meghani contributed to this report.