Margaret Fisher is among the millions of seniors with private, supplemental health insurance that takes care of most of the medical bills Medicare doesn’t cover. If she has a health crisis, she reasons, it won’t become a financial crisis, too.

But officials looking for ways to cut the federal deficit are suggesting that these Medigap policies help explain why the government’s Medicare bill is rising so fast. If these private policies were less generous, they figure, seniors might reduce their trips to the doctor or find cheaper care, which in turn would save the government money.

Fisher, 86, a cancer survivor from Gaithersburg who has had two hip replacements, says that strategy could backfire.

“Some people might really need to go to the doctor and they couldn’t afford it,” she said. “That would be the kicker.”

Medigap insurance is popular because it protects beneficiaries from Medicare’s out-of-pocket expenses that have no cap. During an extended or serious illness, that can run into thousands of dollars. These expenses could include a $1,132 deductible for each hospital stay in 2011 and 20 percent co-payments for outpatient services such as doctor’s visits.

But some budget experts say Medigap may make it too easy for seniors to decide to seek medical care they may not need. The thinking goes that, for example, instead of waiting to see if their condition gets better or if a nonprescription medicine might help, seniors with Medigap policies tend to use more Medicare services than those without such coverage. Getting seniors to delay or forgo some care or find cheaper alternatives could save the government billions of dollars — as much as $53 billion over 10 years, according to the Congressional Budget Office.

For that reason, Medigap has been, and will continue to be, a focus of attention for those seeking to cut the federal deficit.

Here’s a look at some of the issues involved.

What is Medigap?

More than 8 million people — about one in five Medicare beneficiaries — rely on Medigap policies. The plans are sold by companies that can offer up to 10 standard benefit packages set by the federal government. This means that benefits for, say, a Medigap Plan F policy will be the same no matter which company sells the plan, although the costs can vary depending on location and insurers.

More than half of the people who buy Medigap coverage choose one of the two most generous plans. Called C and F policies, they have much higher premiums than the others but pay nearly all of the beneficiaries’ costs. For example, an F plan in Maryland can cost $2,400 in 2011 for a non-smoking 65-year-old, while skimpier plans would be half that.

Why go after Medigap?

Medigap has been targeted because studies have shown that Medicare spends 25 percent more for beneficiaries who have these policies.

Advocates of shifting more costs to seniors suggest that Medicare beneficiaries who are responsible for picking up a portion of the costs will choose the most economical option. For example, a 70-year-old woman with a Medigap plan that doesn’t cover all her costs might take some over-the-counter heartburn medication for stomach pain before seeing a doctor. If that works, she would have saved the federal government money because it would not have paid Medicare’s share of the doctor visit. But if her condition gets worse, Medicare may spend more for her treatment.

What has been proposed?

Congress began looking for savings through Medigap in last year’s health-care overhaul law. One provision of the law directs federal officials to ask the nation’s insurance commissioners to come up with basic cost-sharing changes to C and F plans purchased after 2014 that will encourage the use of “appropriate” doctor services.

In addition, as pressure increases to reduce overall federal spending, President Obama and Congress are trying to wring more savings from Medicare.

Obama released a proposal in September that would have seniors who join Medicare starting in 2017 and who buy C or F Medigap plans pay a surcharge, added to their Medicare monthly premium, equal to 30 percent of that premium. Premiums currently run from $96.40 to $369.10.

A more far-reaching option was suggested last December by the president’s deficit reduction panel: It would prohibit Medigap policies from covering the first $500 of a beneficiary’s share of Medicare medical bills and require the person to pay half of the next $5,000 in costs. That means a senior would have to spend up to $3,000 in addition to his or her Medigap monthly premiums.

Why make a change?

It’s simple: Money.

The deficit reduction commission’s proposal was estimated to save the federal government $38 billion through 2020. The Congressional Budget Office looked at three similar scenarios in a report last summer and found that one would generate more than $53 billion over a decade.

The White House says the president’s surcharge plan would generate $2.5 billion in savings over a decade. Administration officials stressed that the president’s proposal would apply to a relatively small portion of new Medicare beneficiaries and not affect the program’s current 46.5 million members.

What do opponents say?

Many are concerned that seniors faced with medical expenses would put off getting necessary treatment.

Bonnie Burns, a policy specialist at California Health Advocates, a nonprofit advocacy group, and a member since 1990 of a Medigap task force created by the association of state insurance commissioners, says Medigap attracts seniors with modest incomes who may be sicker than the average beneficiary. And it’s unreasonable to ask them to shop for cheaper providers, she said, when doctors don’t know the cost of treatment before they examine patients.

Some also point out that seniors with Medigap have already assumed extra expenses by buying their plans.

Kaiser Health News is an editorially independent program of the Henry J. Kaiser Family Foundation, a nonprofit, nonpartisan health policy research and communication organization not affiliated with Kaiser Permanente.