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Obama officials are blaming their inaccurate or, at least, incomplete assessments on Mr. Clapper’s brief to the White House.

Sen. Dianne Feinstein, California Democrat and chairwoman of the Senate Select Committee on Intelligence, said Mr. Clapper should have waited for more information.

“I think what happened was the director of national intelligence, which we call the DNI, who is a very good individual put out some speaking points on the initial intelligence assessment. I think that was possibly a mistake,” Mrs. Feinstein told the CBS affiliate in San Francisco last week.

The U.S. intelligence official who spoke to The Times defended Mr. Clapper’s action.

The official said that in the first 24 hours after the attack, there were “10 pounds of information that says it’s spontaneous,” including communications intercepts and human sources in the country.

“There’s not a disconnect simply because the preponderance of the information that we had at the time, which was literally being pushed to us — we literally had a bucket of information that suggested it was spontaneous,” the official said.

Other reports that began reaching the DNI indicated otherwise, and the official assessment changed three or four days later.

“Twenty-four hours later, you got two, three, four, five pieces of information, then, yeah, absolutely, we started to revisit it,” the official said. “We have analysts here who work round the clock. And as soon as they have enough, they say, ‘Hey, boss, here’s what it looks like.’ And we changed the assessment.”

The official added: “When one agency, one element, says, ‘We’ve got something that indicates this might not have been spontaneous,’ that’s not ignored. It’s pulled in with the other information.”

The consulate in Benghazi had been attacked at least two times before Sept. 11. In the most serious incident, terrorists placed a homemade bomb at the north gate that blew a huge hole in the wall.