In a move likely to alter treatment standards in hospitals and doctors’ offices nationwide, a group of nine medical specialty boards plans to recommend on Wednesday that doctors perform 45 common tests and procedures less often, and to urge patients to question these services if they are offered. Eight other specialty boards are preparing to follow suit with additional lists of procedures their members should perform far less often.

The recommendations represent an unusually frank acknowledgment by physicians that many profitable tests and procedures are performed unnecessarily and may harm patients. By some estimates, unnecessary treatment constitutes one-third of medical spending in the United States.

“Overuse is one of the most serious crises in American medicine,” said Dr. Lawrence Smith, physician-in-chief at North Shore-LIJ Health System and dean of the Hofstra North Shore-LIJ School of Medicine, who was not involved in the initiative. “Many people have thought that the organizations most resistant to this idea would be the specialty organizations, so this is a very powerful message.”

Many previous attempts to rein in unnecessary care have faltered, but guidance coming from respected physician groups is likely to exert more influence than directives from other quarters. But their change of heart also reflects recent changes in the health care marketplace.