After poring over intercepted electronic communications, informant reports and photographs and video from the scene, American intelligence and counterterrorism officials have concluded that a small number of the local Libyan militia members probably have ties to Al Qaeda in the Islamic Maghreb, the Qaeda affiliate in North Africa. But analysts say they have not found any evidence to indicate that the affiliate ordered or planned the attack.

In his statement, Mr. Turner said that it was unclear who had directed the attack, but that “we do assess that some of those involved were linked to groups affiliated with, or sympathetic to, Al Qaeda.”

At the same time, further details about the attack could lay bare lapses in security that could damage the administration. CNN has reported, from a diary belonging to J. Christopher Stevens, the American ambassador killed in the attack, that he harbored worries about his security. Mr. Williamson, who served as special envoy to Sudan under President George W. Bush, said it was unlikely that Mr. Stevens would not have relayed those concerns to the State Department.

Mr. Romney has been cautious in his public comments about the attack since his initial response, which was criticized by Mr. Obama and Republicans for being premature and unseemly in the face of a tragedy. But Mr. Romney has singled out the administration for its conflicting accounts, and has begun questioning whether it heeded warnings of anti-American attacks in the region, timed to the anniversary of the terrorist attacks on Sept. 11, 2001.

“There are a wide array of reports about warnings, and were they heeded?” Mr. Romney said to reporters on his plane Friday. “We’ll find out whether that was the case or that was not the case.” Similarly, Mr. Romney said it was not yet certain whether the administration’s changing accounts suggested “that they were trying to paper over or whether it was just confusion given the uncertain intelligence reports.”

Peter D. Feaver, a Duke University professor who worked on Mr. Bush’s national security staff, said there was no evidence that the administration was untruthful in its early accounts. But he said it was possible that the White House chose to emphasize certain elements, like the popular outrage in the Arab world against a video mocking the Prophet Muhammad, over other elements, like a possible link between the assailants and Al Qaeda. Such a narrative, he said, would have done less to draw attention away from the uproar over Mr. Romney’s response.