WASHINGTON (AP) -- The White House asserted Sunday that a "common-sense test" rather than "irrefutable, beyond-a-reasonable-doubt evidence" makes the Syrian government responsible for a chemical weapons attack that President Barack Obama says demands a U.S. military response.
As part of a major push to win the backing of a divided Congress and skeptical American public, Obama's top aide made the rounds of the Sunday talk shows to press the case for "targeted, limited consequential action to deter and degrade" the capabilities of Syrian President Bashar Assad "to carry out these terrible attacks again."
At the same time, chief of staff Denis McDonough acknowledged the risks that military action could drag the U.S. into the middle of a brutal civil war and endanger allies such as Israel with a retaliatory attack.
The U.S. is "planning for every contingency in that regard and we'll be ready for that," he told CNN's "State of the Union."
The U.S., citing intelligence reports, says sarin gas was used in the Aug. 21 attack outside Damascus, and that 1,429 people died, including 426 children. The Britain-based Syrian Observatory for Human Rights, which collects information from a network of anti-regime activists, says it has so far only been able to confirm 502 dead.
The Syrian government denies responsibility, contending rebels were to blame.
Obama plans a national address Tuesday night from the White House on Syria, and McDonough was asked whether the president would reveal a direct connect between Assad and the attack.
"The materiel was used in the eastern suburbs of Damascus that have been controlled by the opposition for some time," McDonough said. "It was delivered by rockets - rockets which we know the Assad regime has and we have no indication that the opposition has."
McDonough also cited a DVD compilation, released Saturday by a U.S official, of videos showing attack victims. The DVD was shown to senators during a classified briefing on Thursday.
"We've seen the video proof of the outcome of those attacks. All of that leads to a quite strong common-sense test irrespective of the intelligence that suggests that the regime carried this out. Now do we have a picture or do we have irrefutable beyond-a-reasonable-doubt evidence? This is not a court of law and intelligence does not work that way. So what we do know and what we know the common-sense test says is he is responsible for this. He should be held to account."
Recent opinion surveys show intense American skepticism about military intervention in Syria, even among those who believe Syria's government used chemical weapons on its people.
Congress resumes work Monday after its summer break, but already a heated debate is underway about Syria.
On Wednesday, the first showdown Senate vote is likely over a resolution authorizing the "limited and specified use" of U.S. armed forces against Syria for no more than 90 days and barring American ground troops from combat. A final vote is expected at week's end.
A House vote appears likely during the week of Sept. 16.
A survey by The Associated Press shows that House members who are staking out positions are either opposed to or leaning against Obama's plan for a military strike by more than a 6-1 margin. The Senate is more evenly divided ahead of its vote.
Nearly half of the 433-member House and a third of the 100-member Senate remain undecided.
Complicating the effort in the Senate is the possibility that a three-fifths majority may be required. Republican Sen. Rand Paul of Kentucky says he is going to filibuster.
Still, Sen. Harry Reid, the Democratic leader, has predicted, "I think we're going to get 60 votes,"
Another bipartisan, classified briefing for Congress is set for Monday. McDonough plans to meet Tuesday with the House Democratic Caucus, whose support could be crucial as Obama faces opposition from House Republicans.
Obama's national security adviser, Susan Rice, plans to discuss Syria in a speech Monday at the New America Foundation.
In addition to the classified briefing scheduled Monday for House members and senators on Wednesday, national security adviser Susan Rice will meet separately with the Congressional Black Caucus, the White House said.
Vice President Joe Biden planned to host a dinner Sunday night for a group of Senate Republicans, and lawmakers should expect more phone calls from top officials.