AS THE ADMINISTRATION casts about for ways to lighten the federal budget, its attention is naturally drawn to the Medicare program which, next year, will spend over $50 billion on health care services. Since there is no miracle cure for the high cost of modern medicine as applied to a fast-growing population of elderly, the only way to more of their own medical bills.

Medical care, however, has become so expensive that most elderly and disabled people already find it a strain to cover the part of medical costs that isn't covered by Medicare. The very poor can also get help from the Medicaid program, but most people can't qualify unless they have used up almost all of their savings on medical bills. This has led budget planners to think about schemes that would deny full coverage to people with relatively high incomes -- in other words, introduce a "means test."

Health and Human Services Secretary Richard Schweiker, however, told a congressional panel this week that he opposes such an idea and will strongly advise the White House not to propose it. That's good advice. There are many practical difficulties with this approach, not the least of which is that to make a proposal politically acceptable, the income limit would have to be set so high that it wouldn't save much money.

But it's not the practical difficulties that should give the administration pause. It should look instead at why a lower limit, or any limit at all, would meet with huge political resistance. Most people, with good reason, don't look at Social Security and Medicare as gifts dispensed by a beneficent government. They look at universal retirement and health insurance as basic services that government should provide its citizens in return for the taxes they pay. True, many people could save up to buy health insurance for their old age -- though they'd pay more for it than Medicare does because of the high overhead on privately marketed plans. But many others -- no matter what their prior earnings -- would fall between the cracks.

There are numerous hazards that can't be planned for -- unemployment, divorce, desertion, competing money demands for a child's education or a parent's care. Most threatening is the substantial risk that, just when health coverage is needed most, a private insurer will decide that a person is no longer a "good risk." Full insurance is something that only government can provide. That's why, when the White House reviews its Medicare options, a means test should be ruled out.