The phrase "be in operation" refers to something that is functioning or working. Its antonyms can include "out of operation," which means something is not functioning or working properly. Another antonym for "be in operation" is "shutdown," which implies that something has been deliberately turned off or closed down. Similarly, "defunct" suggests that something is no longer in use or has ceased to exist. "Inactive" can also serve as an antonym, indicating that something is not currently in use or functioning. Other possible antonyms could include "non-functional," "dormant," or "suspended," each indicating different levels of inactivity or disuse.