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.

Now, the impact of two major proposals in the House plan that are ­intended to level the playing field — a one-time luxury tax on high-priced providers and restrictions on contract negotiations — is in doubt after lobbying by hospitals.

The Senate proposal, meanwhile, takes a more indirect approach to the problem, including establishing ­another commission to dig deeper for the reasons for price differences and requirements to publicly track price inequities.

House and Senate leaders will not comment on the status of negotiations aimed at producing a compromise bill ­before the legislative session ends this month. But Governor Deval Patrick and Senate President Therese Murray have made clear that they oppose the House plan to tax providers whose prices are at least 120 percent of the statewide median and redistribute the money to struggling hospitals, making approval in its current form ­unlikely.