If Social Security paid you back all the money you'd ever put in plus interest, how much would it be? Enough to live on in your old age?

Emphatically not. To finance your own benefits, at levels to which we've become accustomed, payroll taxes over the years should have been more than three times as high as they actually were. A good part of every Social Security check comes from other people's contributions, rather than our own.

Social Security started in 1937, if you had paid the maximum into the system since that date, and retired at the end of this year, your 40-year contribution would be only $8,728.35. Employers would have made matching contributions, for a total of $17,456.70.

Assuming those contributions earned interest at prevailing passbook savings rate from 1937 to present your entire Social Security account would come to roughly $28,000.

How much retirement income can you get for $28,000? An annuity from an insurance company would pay a 65-year-old man about $241 a month, and a woman, $213. But Social Security pays twice as much. Starting in January, 1978, a 65-year-old-man can retire on $459.80 a month. If married, the joint check would come to $689.70.

To get a lifetime annuity, with joint and survivors checks similar to those offered by Social Security, a 65-year-old would have to pay an insurance company around $93,500.

But even this understates the extent to which Social Security payments are subsidized. Under the program, you're also eligibe for Medicare, death and disability insurance, and cost of living increases. If the price of insuring these benedits were deducted from your total contribution of $28,000 what would be left for retirement income? Not much.

In other words, it's wrong to think of Social Security as an insurance program. Insurance is structured only to repay what you put in, plus interest. If the annuity isn't enough to live on, that's your problem. Social Security, on the other hand, takes into consideration what you need to live on, and pays accordingly. If you yourself haven't paid enough to finance benefits, others are taxed to supply the money.

At bottom, Social Security is a massive income-transfer system like welfare. Those with earnings are taxed to provide benefits for those who used to be self-supporting but no longer are - widows, orphans, the disabled, retired people without much income.

How much you get is decided by how long you worked and how much you made. But that's the only link between earnings and benefits.

Defining Social Security as a tax program, aimed at helping people without earnings, raises questions about a change in benefits just voted by the House of Representatives. The House proposed paying Social Security to everyone in the system over 65, no matter how much he earns.

But do you want your personal payroll taxes to rise, in order to pay an extra $8,300 a year to doctors, lawyers, businessmen and others with the opportunity to make good money in their later years? At present. Social Security payments are reduced by $1 for each $2 or earnings over $3,000. The administration supports a modest increase in allowable earnings, but opposes universal payments.

Two reasons it has always been easy and popular to raise Social Security benefits are, first, that Americans haven't objected to payroll taxes, and second, taxes were small in relation to benefits. Between 1972 and 1976, voters cheered as benefits rose at a rate 49 per cent higher than the cost of living. Were those enormous increases really justified? Maybe so, maybe not. But if they have been financed by income taxes, which people do object to paying, the benefit levels might at least have been scrutinized more carefully.