For decades, the prices Medicare pays doctors for different medical services have been largely decided not by Medicare itself, but by a powerful industry group, the American Medical Association.

An A.MA. committee meets in secret to determine the difficulty and time demands of each type of medical visit, test and procedure, and then recommends to Medicare how much doctors should be paid for performing them.

And for decades, critics have complained that this process unfairly rewards surgeons and other specialists, at the expense of primary care physicians and other generalists.

Medicare officials have been loath to change it because it has spared them from needing their own staff and budget to make such pricing decisions, along with the unpleasant politics of adjudicating conflicts between competing groups of physicians.

But a change buried inside a 1,803-page proposed regulation published last Monday suggests the Trump administration would like to move away from this longstanding system. If finalized, it could begin overturning a process that has entrenched pay advantages for certain kinds of doctors.

“We’re modernizing Medicare by correcting outdated assumptions in how physician services are valued,” said Chris Klomp, a deputy administrator of the Centers for Medicare and Medicaid Services, in an email.