The White House chief of staff, Denis R. McDonough, said Sunday that the American people’s skepticism about the prospect of military action in Syria was “understandable” after a decade of war in Iraq and Afghanistan, but that such a strike would be far different from those wars.

Mr. McDonough appeared on all five major Sunday morning news shows to make the administration’s case that Congress should authorize an airstrike against the forces of President Bashar al-Assad of Syria. Mr. Assad, for his part, said in an interview with Charlie Rose of CBS News that his government was not behind a chemical attack that killed hundreds of civilians and injured many more. In the interview, to be broadcast on Monday, Mr. Assad also said that Syria might retaliate if attacked.

Mr. Assad, who previously denied he was behind the attack, “suggested that there would be, among people that are aligned with him, some kind of retaliation if a strike was made,” Mr. Rose said on CBS’s “Face the Nation.” Allies of the Assad government include Iran and Hezbollah, the militant Islamist group based in Lebanon.

Mr. Rose added, “He had a message to the American people that it had not been a good experience for them to get involved in the Middle East in wars and conflicts.”