WASHINGTON — When career employees of the Environmental Protection Agency are summoned to a meeting with the agency’s administrator, Scott Pruitt, at agency headquarters, they no longer can count on easy access to the floor where his office is, according to interviews with employees of the federal agency.

Doors to the floor are now frequently locked, and employees have to have an escort to gain entrance.

Some employees say they are also told to leave behind their cellphones when they meet with Mr. Pruitt, and are sometimes told not to take notes.

Mr. Pruitt, according to the employees, who requested anonymity out of fear of losing their jobs, often makes important phone calls from other offices rather than use the phone in his office, and he is accompanied, even at E.P.A. headquarters, by armed guards, the first head of the agency to ever request round-the-clock security.

A former Oklahoma attorney general who built his career suing the E.P.A., and whose LinkedIn profile still describes him as “a leading advocate against the EPA’s activist agenda,” Mr. Pruitt has made it clear that he sees his mission to be dismantling the agency’s policies — and even portions of the institution itself.