While the intelligence does not tie Mr. Assad directly to the attack, these officials said, the administration said the United States had both the evidence and legal justification to carry out a strike aimed at deterring the Syrian leader from using such weapons again.

A critical piece of the intelligence, officials said, is an intercepted telephone call between Syrian military officials, one of whom seems to suggest that the chemical weapons attack was more devastating than was intended. “It sounds like he thinks this was a small operation that got out of control,” one intelligence official said.

Image “Learn the lessons of Iraq, because people remember the mistakes that were made in Iraq.” ED MILIBAND Leader of Britain’s opposition Labour Party Credit... UK Parliament,via Reuters TV

But Republican lawmakers said White House officials dismissed suggestions that the scale of the attack was a miscalculation, indicating that the officials believe Syria intended to inflict the widespread damage.

“I’m comfortable that the things the president told Assad not to do he did,” said Senator Lindsey Graham, Republican of South Carolina, who took part with seven other Republican senators in a separate briefing by the White House chief of staff, Denis R. McDonough.

Among the officials on the conference call were Secretary of State John Kerry; Defense Secretary Chuck Hagel; the director of national intelligence, James R. Clapper Jr.; and the national security adviser, Susan E. Rice. It was unclassified, which means the administration gave lawmakers only limited details about the intelligence they assert bolsters the case for a military strike.

Before the call, however, some prominent lawmakers expressed anger that the White House was planning a strike without significant consultations with Congress. “When we take what is a very difficult decision, you have to have buy-in by members and buy-in by the public,” Representative Mike Rogers, the Michigan Republican who is chairman of the House Intelligence Committee, said Thursday on MSNBC. “I think both of those are critically important and, right now, none of that has happened.”