The exchanges will mostly steer clear of many of the nation’s top academic hospitals because those providers tend to provide more extensive and expensive care, industry officials said. Insurers also are likely to include in their networks the doctors they deem the most cost effective.

The Medical Group Management Association in September surveyed nearly 48,000 physicians about the health care exchanges and found that less than 30 percent of those doctors planned to participate in the exchanges. Another 40 percent said they would consider joining an exchange, the survey showed.

Nearly 60 percent of the doctors who decided not to participate in the exchanges said they ruled it out because they feared that low reimbursement rates from exchange-purchased insurance plans would threaten their practices.

“Cost is a huge factor,” Anders M. Gilberg, a lobbyist with MGMA. “The plans have made no secret of the fact that the way they are offering lower premiums to patients and benefit options on the exchanges is either by reducing reimbursement rates to physicians or narrowing the networks or controlling the number of physicians. They are contracting with fewer physicians and the reimbursement rates are lower relative to plans outside the exchanges.”