Secretary of State John Kerry and Defense Secretary Chuck Hagel testifying before the Senate Foreign Relations Committee on Tuesday. Chip Somodevilla/Getty Images

Secretary of State John Kerry told the Senate Foreign Relations Committee on Tuesday that refusal to launch a limited, punitive military strike on Syria would undermine U.S. credibility, including its pledge to prevent Iran from acquiring nuclear weapons. He and Defense Secretary Chuck Hagel testified in support of President Barack Obama’s push for the United States to intervene in Syria’s ongoing two-year civil war.

"This is not the time for armchair isolationism," Kerry said. "This is not the time to be spectators to slaughter."

Obama has urged Congress to act quickly on a resolution authorizing action against Syria, as he ramps up his effort to win support for strikes against President Bashar al-Assad's forces in response to the alleged Aug. 21 chemical weapons attack that the U.S. says killed nearly 1,500 people.

Facing tough questions from the committee, Kerry said the debate about military strikes against Syria is not about Obama's "red line" that weapons of mass destruction cannot be tolerated.

Instead, Kerry argued, "this debate is about the world's red line." He said it is "a red line that anyone with a conscience ought to draw."

Only hours earlier, after meeting with Obama, House Speaker John Boehner said he believed responding with military force to an alleged chemical attack in Syria is "something the United States as a country needs to do."

Boehner said, "I'm going to support the president's call for action. I believe my colleagues should support this call for action."

During the meeting with congressional leaders at the White House, Obama said he was confident that Congress would vote in favor of military action and said the United States had a broad plan to help the rebels defeat Syrian government forces.

"What we are envisioning is something limited. It is something proportional. It will degrade Assad's capabilities," Obama told reporters. "At the same time, we have a broader strategy that will allow us to upgrade the capabilities of the opposition."

House Minority Leader Nancy Pelosi also expressed support for the president's call for action, and reiterated that any planned strike would be of "short duration."