The federal Food and Drug Administration said Tuesday that it would take steps to more stringently regulate three of the most potent forms of medical radiation, including increasingly popular CT scans, some of which deliver the radiation equivalent of 400 chest X-rays.

With the announcement, the F.D.A. puts its regulatory muscle behind a growing movement to make life-saving medical radiation  both diagnostic and therapeutic  safer.

Last week, the leading radiation oncology association called for enhanced safety measures. And a Congressional committee was set to hear testimony Wednesday on the weak oversight of medical radiation, but the hearing was canceled because of bad weather.

The F.D.A. has for weeks been investigating why more than 300 patients in four hospitals were overradiated by powerful CT scans used to detect strokes. The overdoses were first discovered last year at Cedars-Sinai Medical Center in Los Angeles, where patients received up to eight times as much radiation as intended.