Behavior analysis, as it suggests, focuses on treating behavioral problems (both pure and those secondary to psychiatric disturbance or cognitive/intellectual deficits) from a purely behavioral perspective/lens. Functional analaysis, gathering of data to establish trends, and then a subsequent intervention program or plan that utilizes various forms of operant learning are then applied. Psychologists can do this (I did for a time), although BAs tend to be a bit more formally edcuated on the process.
Psychologist's scope of practice is much, much larger than this. You can visit the Ph.D./Psy.D. board to learn more about the practice of psychology and tghe various different roles and jobs we have.