Last year, after protests by the elderly against premiums forced repeal of the 1988 Medicare "catastrophic-illness" insurance program, it was widely accepted that Congress would be more cautious the next time it voted new medical benefits for the aged.

That reaction may be understandable, but a new Census Bureau report provides overwhelming evidence that eventually the government, the private sector, or both will have to face the problem. The demographics show that the nation will need some insurance mechanism to finance at-home care and nursing-home care for the aged.

The report looked at people 15 years and older, not living in institutions, who need assistance from someone else with one or more everyday activities.

Of about 186 million people 15 and older in 1986, about 8.2 million needed help with one or more activities for a health condition of three months or longer.

Some needed help only with cooking, housework or keeping track of bills. But 3.2 million needed help with personal care activities such as eating, dressing, using the bathroom or bathing. And 5.2 million needed help with getting around outside (this group includes some in the personal care category).

The figures show that the older a person is, the more likely he or she needs assistance. Only 2.4 percent of those from 15 to 65 needed help with one or more types of activities, and only around 10 percent of those 65 to 74, but above that age, the proportion needing help increases sharply. For those 80 to 84 it is 24 percent, and among those 85 and over, it skyrockets to 45 percent.

Once this was not so much a problem because life expectancy was not that great and the traditional family provided support systems for elderly relatives.

But the number of people 85 and over is projected to shoot up from about 3 million today to more than 6 million by 2010 and more than 12 million by 2040.

Of all those requiring assistance, the Census Bureau report found that 5.6 million lived with relatives and 2.6 million alone or in some other arrangement, such as with non-relatives.

With the costs of a nursing home in the range of $30,000 a year today, the Census Bureau figures indicate that the nation may have to construct some insurance system to care for future multitudes of frail, elderly people.