When legislation to protect 32 million elderly and disabled Americans against "catastrophic" medical costs passed the Senate, Sen. David Durenberger (R-Minn.) pointedly noted that it contains two striking innovations in the nation's approach to social programs such as Social Security and Medicare.

Durenberger, who was floor manager of the bill on the Republican side, said that for the first time, "You have a major new benefit being added to the social insurance program with all of the costs of that benefit being borne by those who benefit from it."

Moreover, he said, "For the first time, we are income-testing part of the social insurance program." In other words, while all Medicare enrollees will be eligible for the new "catastrophic" benefits regardless of income, the amount of premiums paid by each individual to cover the costs of the new benefits will be based on income.

These innovations represent a significant change and could portend further moves along the same lines in the future -- such as paying for nursing home care, which Medicare does not cover under the bill, by a similar mechanism.

Durenberger, Finance Committee Chairman Lloyd Bentsen (D-Tex.), the bill's chief sponsor, and others also suggested that by approving the measure, Congress is sending a message to Americans: That while constrained by money problems, Congress is increasingly determined to make sure all Americans eventually obtain some reasonable measure of health care -- probably by using both the private and public sectors to plug gaps incrementally, rather than through any overarching national health insurance scheme.

Sponsors of the House version, Reps. Fortney H. (Pete) Stark Jr. (D-Calif.) and Willis D. Gradison Jr. (R-Ohio), sent out similar signals during House deliberations.

The current catastrophic measures, taking a step in that direction, greatly expand the range of protection for elderly and disabled Medicare beneficiaries who have extraordinarily high medical costs that can easily bankrupt a family.

Under the Senate bill, Medicare beneficiaries would be guaranteed up to 365 days of free hospital care a year after payment of an initial deductible of $540. Only 60 days are free now. Few Medicare beneficiaries -- less than 200,000 -- normally stay more than 60 days during a spell of illness, but if they must, the costs can be devastating.

The Senate bill also provides that no Medicare beneficiary need pay more than $1,850 a year (including the $540 hospital deductible) for out-of-pocket payments for deductibles and copayments for Medicare services other than prescription drugs.

This does not mean that Medicare will cover all nondrug medical expenses above $1,850; it will not pay anything for services that Medicare does not normally cover, such as permanent full-time, at-home nursing or maintenance care, or long-term stays in a nursing home. Nor would it pay for doctor charges in excess of the amount allowed by Medicare for a given treatment.

But for a variety of services that are covered, this protective guarantee will apply. About 5 percent of Medicare's 32 million beneficiaries are estimated to exceed the out-of-pocket threshold.

A drug benefit to be phased in over several years, figured entirely separately from the $1,850 threshold, would cover 80 percent of the cost of medically prescribed outpatient maintenance drugs in excess of $600 a year. About 5 million beneficiaries are expected to receive this benefit annually. Medicare currently does not pay for outpatient drugs.

The House bill includes similar provisions, in many cases more generous. There are a number of smaller benefit improvements in both bills as well.

Under the Senate bill, the provisions are being financed entirely from new premiums that will be paid by Medicare beneficiaries. All Medicare enrollees will pay a $4-a-month extra premium for the basic new benefits plus a small amount extra (60 cents a month in 1990, rising to $3.80 by 1993) for the prescription drug benefit.

In addition, about a third of the enrollees with middle to higher incomes will pay a "supplemental" income-based premium as high as $800 a year in 1988 for an individual with $60,000 total income. But for most enrollees it would be much less -- about $246 a year for a retired couple with $40,000 total income, according to estimates by the American Association of Retired Persons (AARP). The remaining two-thirds of enrollees would not pay any supplemental premium because their incomes are too low.

About 55 percent of the estimated $24 billion, five-year (1988-92) revenues from the premiums will come from the supplemental, income-tested premium, the rest from the flat monthly premiums.

Since Social Security began in 1935, and since Medicare was added in 1965, neither the amount of Medicare premiums paid (for participation in the doctor-insurance portion, Part B) nor eligibility for Medicare or Social Security benefits has ever been means-tested.

Moreover, benefits have never been financed entirely or even primarily from either premiums or tax payments paid by the current retired beneficiaries. It is the nonretired persons who are currently in the work force who pay for the vast bulk of Social Security and Medicare costs, through the Social Security payroll tax and through general taxes from which the Treasury pays huge subsidies to Medicare.

Social Security and Medicare have never had a means test because Social Security was originally seen as a system that could provide real, guaranteed security in old age only if it did not depend on the individual first losing his possessions and falling into poverty.

Franklin D. Roosevelt and his advisers feared that a program based on need -- welfare -- would be subject to repeated slashes by Congress whenever there was any financial pressure. So he wanted to set up a contributory system with benefits received automatically by all to prevent people from going into poverty, rather than one that would only rescue them afterwards.

The premium for Medicare and the payroll taxes that workers pay to obtain future eligibility for Social Security and Medicare were seen, in a sense, as insurance premiums, and in the insurance world premiums are not based on income.

Historically, the elderly have been poorer than other groups in the population (though that is less and less the case) and as a group they were unable to pay premiums high enough to finance added benefits for all elderly who might need them.

The financing of the catastrophic-illness program entirely through premiums imposed on the 32 million Medicare enrollees, with 55 percent of the revenue coming from an income-related premium, breaks with tradition. Many groups representing the elderly were not happy with charging the elderly for the whole bill.

But the turmoil surrounding the federal budget deficit proved decisive. Faced with huge deficits and with the Reagan administration determined to oppose any general tax increases, members of Congress realized there was no extra money in the Treasury to subsidize catastrophic-illness benefits. If they wanted the protection, the aged and disabled would have to pay for it entirely by higher Medicare premiums. The AARP and the National Council of Senior Citizens decided that on balance they would support the bill, despite their reservations about making the beneficiaries pay for the whole package.

The question turned on what to do about the millions of low-income elderly. If a flat premium, the same for all 32 million Medicare enrollees, were to be imposed, it could come to several hundred dollars a year or more, depending on benefits to be granted, something a person with income of only a few thousand dollars a year could ill afford.

From the start, the congressional sponsors were convinced they would have to raise part or all of the needed money through an income-based tax or premium on the elderly, and it was Bentsen who first came up with the idea of a two-premium system, with all enrollees paying a basic monthly premium and higher-income ones paying an added one based on income.

The congressional sponsors argued, however, that their plan would not "means test" the system. The classic means-test concept, Stark said repeatedly, is that if you are not poor, you don't get any benefits. Under the House and Senate bills, everyone gets benefits -- even the rich. The only thing that is based on income is the premium.

"It's not a means test unless eligibility for benefits or the amount of benefits depend on current income at the time people apply," said Robert M. Ball, a former commissioner of Social Security and one of the most influential Democratic voices on these programs.

Supporters of the income-based premium, in many cases liberals who had fought such notions in the past, seem to have concluded that after 50 years of Social Security and 20 years of Medicare, they need no longer fear conversion to a means-tested welfare program for which only the poor are eligible.

In one way, the bill's approval may be more significant than just the immediate benefits it provides. There is a growing consensus on Capitol Hill that in a rich nation, everyone should have health care and that Congress must take action to ensure it. Currently, 37 million people have no health insurance. But there is no consensus on what steps to take, and proposals for a national health system have failed to win wide support.

For several years, however, there's been a strong bipartisan effort to fill in the gaps on an incremental basis, with Bentsen, Durenberger, Gradison, Stark, Rep. Henry A. Waxman (D-Calif.), Sens. Robert J. Dole (R-Kan.), Edward M. Kennedy (D-Mass.), John Heinz (R-Pa.), George J. Mitchell (D-Maine), John H. Chafee (R-R.I.), Lowell P. Weicker Jr. (R-Conn.) and others teaming up to plug gaps in health coverage when and where possible.

Catastrophic coverage for Medicare beneficiaries is one example. Included in various bills are provisions sponsored by Waxman, Sen. Barbara Mikulski (D-Md.), Bentsen, Mitchell and others to make sure that the spouse of a person in a nursing home doesn't fall into poverty before Medicaid starts paying the bill.