As legislative leaders close in on a major health care cost-control bill, key efforts to attack one of the most-cited reasons for rising medical spending — the market power of caregivers who demand high prices for their services — appear to be in jeopardy.

In a 2010 report, Attorney General Martha Coakley blamed the leverage of the best-paid providers as a main driver of health care costs. She found that insurers pay some hospitals and doctors twice as much money as others for similar care, because they have name-brand recognition or geographic dominance. Legislators, too, ­believed that provider market clout might be driving up premiums for small businesses, and they directed a commission to find solutions.