(MONEY Magazine) – While traditional fee-for-service plans sometimes give doctors an incentive to prescribe more treatment than is necessary, many managed-care plans actually have an incentive to undertreat you -- since it maximizes their profits. Here are some ways to make sure you and your family get the best care:

-- STUDY THE PLAN THOROUGHLY. When you are choosing between plans, start by reading the booklet that describes details of the plan's coverage. Check out the fees, of course, in order to estimate your likely out-of-pocket costs. But also find out whether the plan will treat any pre-existing conditions you may have (HMOs usually will do so, but other types of plans may not) and whether it will cover things like mental health care and ''experimental'' treatments such as bone marrow transplant. If the plan relies on a network of physicians, ask whether it has the specialists on staff you need and what restrictions it places on your ability to seek care outside the network. Mike Doyle of Champaign County Health Care Consumers, a consumer's group in Champaign, Ill., suggests you also call the plan and ask how many primary-care physicians and how many specialists are on its staff. The numbers should be roughly equal, Doyle says, for a good balance between basic and specialized medical care.

-- FIND A DOCTOR YOU LIKE, OR GET YOURS TO JOIN. If the plan relies on a limited group of physicians, get the names of three doctors from the network's enrollee service representative or from friends who are plan members. Then visit each of them (typical cost at an HMO: $5 to $15 per visit). Choose one with whom you have rapport. Or, if you would prefer to keep seeing a non- network physician who is already treating you, ask him or her to join the plan (the doctor can find out the requirements by calling the plan's chief of medical staff). If your doctor is reluctant to join and you will be reimbursed at a lower rate if you continue to see him, ask him to share the loss by reducing his fee.

-- BE ASSERTIVE IN SEEKING CARE YOU NEED. Many patients complain that they & have trouble getting their plans to perform costly tests, for example. If you can't get a test or procedure, ask the plan for a second opinion or a new doctor.

-- APPEAL ANY DECISION YOU DISAGREE WITH. A study by the General Accounting Office last year found that fewer than 12% of people denied coverage by utilization-review companies appeal but that more than one-third of those who do protest have their requests granted. The appeals procedure will be spelled out in your coverage booklet. If you are refused a treatment and can afford the delay, ask the plan for a written explanation of its refusal so you can rebut it. And keep careful records, including copies of all correspondence and a phone log showing the date, the name of the person you spoke to and what was said.

-- ASK FOR REVIEW BY A ''SPECIALTY-MATCHED PHYSICIAN ADVISER,'' if your appeal concerns proposed treatment by a specialist. That way, if you're seeking permission to see an orthopedic surgeon for a diagnostic knee procedure, you can be sure that another orthopedic surgeon will judge the case.

-- SEEK HELP FROM ANYONE WHO WILL GIVE IT. Even in an HMO, where the doctor works for the plan instead of for you, he or she is your most important ally. Ask the doctor to explain clearly to the plan why the recommended treatment is needed and to provide paperwork, studies or records to support your case. If you're in a hospital, you can seek the same help from the managed-care department, patient advocate, social worker or case manager. Don't neglect your employer, either, if yours is a company-paid plan, since the company will sometimes go to bat on your behalf. ''We get a number of noes changed to yesses,'' says William Gebhardt, director of human resources at Jacobs Engineering Group in Pasadena, which instituted a PPO in 1989.

-- GET TREATMENT FIRST AND FIGHT ABOUT IT LATER, if you feel your health is threatened. Appealing a managed-care decision typically takes 30 days. If you lose, try to persuade your doctor or hospital to lower the bill. -- R.S.