The longtime member of the Secret Service -- who became director in September 2022 -- addressed Saturday's shooting with ABC News correspondent Pierre Thomas on Monday. As Cheatle put it ... she has taken full responsibility for the attack, making it clear the incident should've "never happened."

She added ... "The buck stops with me. I am the director of the Secret Service, and I need to make sure that we are performing a review and that we are giving resources to our personnel as necessary."

Cheatle then shed light on Saturday's tragedy, which left 45 shot in the ear and another dead at a rally in Pennsylvania. According to the director, the incident took place in a short period of time ... which included finding, identifying, and neutralizing Thomas Matthew Crooks, who has been identified as the shooter.

KC did seem to point some of the blame at local police, however ... as she confirmed that they were inside and around the building while the shooter fired shots at Trump and his rallygoers.

She continued ... "There was local police in that building -- there was local police in the area that were responsible for the outer perimeter of the building."

As to whether Cheatle plans to resign in the aftermath of the attack? She said she plans to remain in her role ... but is expected to testify before the House Oversight Committee next week.