The Secret Service’s acting director acknowledged on Friday that when he told congressional investigators that local law enforcement snipers should have been able to see the gunman who shot former President Donald J. Trump at a rally, he did not have details from the snipers themselves on their locations.

Rather, the acting director, Ronald L. Rowe Jr., said his understanding of where the local snipers were positioned was based on a review of the agency’s operational plan and his own agents’ descriptions of what they saw.

Local law enforcement officials have vehemently contested his account, saying the Secret Service appears to be trying to shift blame for the failures that led to the assassination attempt last month in Butler, Pa., even as it claims to take responsibility for them.

Mr. Rowe’s explanation came as he took questions from reporters Friday afternoon during the Secret Service’s first news conference about the assassination attempt.

The sharply diverging accounts about what led to the security lapses have fueled tensions between the Secret Service and local officials just as the presidential campaign enters its final stretches, when the agency must work even more closely with local law enforcement.

In testimony earlier this week, Mr. Rowe told senators that the local snipers would have been able to see the gunman, who was on the roof of the building in front of where they were posted, if they had looked left out the window.