Congress' new quick-fix solution to revive the financially anemic Social Security system may need another booster-shot - sooner than we think.

Although the sharp rise in payroll taxes was billed as a move that would keep the system vibrant for generations, many analysts believe the patient will need further treatment again, possibly by the mid-1980s. And this time, it will take major surgery - not just an infusion of money.

The reason is a simple one. Although the bill passed last month raised revenues enough to stave off imminent bankruptcy, it didn't solve any of the system's structural problems, which are really the cause of the financial difficulties of the past few years.

The tax increase is sufficient to get the Social Security system through the rest of this decade. But after that, the question of whether there will be enough to cover benefits depends largely on how the economy does. And many analysts believe it won't perform as well as the bill's architects predict.

Finally, there are genuine questions about whether the public will stand for the new tax increases for very long. Key congressional leaders already expect a taxpayers' revolt over the boosts - even though the really big jumps carefully were postponed until after this November's election.

As a result, many officials already are predicting Congress will have to return to the Social Security question in a few years - possibly for a major overhaul that would shift part of the tax load to the income tax, mandate participation by government workers and slow the growth of benefits.

Rep. Al Ullman (D-Ore.), chairman of the House Ways and Means Committee, already has suggested Congress will have to find "a better financing mechanism" to replace some of the payroll tax increases it has scheduled for the 1980s.

And some private tax experts also see further changes ahead. "There are all kinds of structural problems they haven't faced yet," says Rudolph G. Penner, a former Office of Management and Budget economist who now heads the tax study program at the American Enterprise Institute.

The situation is ironic because, at least at first blush, the bill passed in December would seem to contain enough payroll tax increases to overcome any financial disaster. Over the next eight years, the measure will triple the maximum tax burden for higher-salaried workers and their employers.

The payroll tax last year amounted to 5.85 per cent of the first $16,500 of a worker's salary - for a maximum tax of $965. By 1986, the tax will soar to 7.15 per cent of the first $40,200 in earnings - a maximum of $2,874. (And that doesn't count this year's rise, which is based on earlier legislation.)

According to Congress' own figures, these tax increases ought to be enough to keep the system's special retirement fund solvent until the year 2031, the disability fund until 2005, and the Medicare fund until 1989 - effectively buying the lawmakers time to consider more fundamental "reforms."

But those projections assume that the inflation rate will slow to 4 per cent from its present 6 per cent pace, that wage increases will ebb to 5.75 per cent from 8.4 per cent now, and that the jobless rate, now 6.9 per cent, will drop to 5 per cent - all forecasts that, to say the least, are now uncertain.

Analysts say if inflation proves even slightly worse than expected - or unemployment remains higher - the disability and retirement funds could run out of money, forcing Congress to go back and bail the system out again. And if that happens, tax increases alone may not be enough to do the job.

The fundamental problem is that the Social Security system no longer is simply a retirement subsistence fund, as it was intended to be in the 1930s. Instead, it's grown into something approaching a full-fledged pension - and an amalgam of disability and health benefits that go far beyond the scope of the payroll tax to finance.

Indeed, benefit levels have soared so sharply in recent years that many private companies are complaining the Social Security system is driving their own pension plans out of business. (Company plans generally provide a specific percentage of an employee's last wage level - minus what he gets from Social Security. But government benefits now are so high, it isn't always worht it for a firm to maintain its own plan.)

The overgrowth began in the heady, socially conscious 1960s, whe Congress added dozens of new benefits to the basic pension plan - many of them in expensive disability programs that have outstripped the trust fund's capability. It also stretched the payroll tax to finance Medicare.

But the ultimate blow came in late 1972, when - in an obvious political gesture - the lawmakers approved an election-year package that not only boosted all benefits by a whopping 20 per cent, but also adotped a double-dip cost-of-living adjustment that tied benefits and taxes to inflation and wage gains.

Conservatives warned repeatedly that the double-dip inflation formula was risky, but they were largely ignored. Then came the 1973-74 bout of double-digit inflation, followed by the worst recession in 30 years and the financing system effectively caved in. Something clearly had to be done.

In the bill passed in December, Congress did change the benefits formula to eliminate the double inflation adjustment, but it sidestepped other fundamental "reforms." In effect, the system has most of the same faults it had before the latest rescue effort. All the lawmakers did was buy a little time.

Moreover, it's still unclear whether the public will accept the new tax increases - at least without fighting. With this year's House and Senate races doubtless in mind, the lawmakers postponed the first of the tax increases until 1979 - and they won't really begin to take off until the mid-1980s.

Still, many legislators expect their constituents to begin protesting even the relatively modest payroll tax boost that went into effect last week - even though it actually was mandated by an earlier bill. (Last week's jump pushed the tax rate to 6.05 per cent and the wage base to $17.700.)

And supporters of the program fear that unless the larger, mid-1980s tax increases can be headed off, they may dilute support for Social Security among the politically articulate midde- and upper-income workers - the very group most needed to maintain the program in coming years.

Opinion polls already show that voters are divided over the Social Security issue. While most want something done to make the program solvent agains, they're split almost evenly over whether Congress should raise taxes in order to do the job.

It's not at all clear what the lawmakers will do the next time they consider the program. The most radical proposal are to end the payroll tax and finance benefits instead with the less onerous income tax. There also are suggestions to transfer the system's health programs into the general fund.

The blue-ribbon Social Security Advisory Council recommended in 1975 financing the hospital insurance portion of the Medicare program with the income tax, and using that portion of the payroll tax to bolster the disability and retirement funds. But Congress decided against in in last year's bill.

(The idea of using general income tax revenues to underwrite the Social Security program makes sense from an economic viewpoint because the income tax is considered less "regressive" than the payroll tax, which hits the working poor proportionately harder.

(But it's difficult politically, largely because of the myths that persist. Many voters still view the system as a retirement program, with benefits fully financed by the taxes they paid in. Actually, there's no such tight link: Benefits are set independently, financed by the current year's payroll taxes.)

What mot likely will happen will be that Congress will try again to hedge the issue by moving cautiously toward one or more compromise proposals. Those considered most promising include:

Requiring federal, state and local government workers, now exempt from Social Security, to participate in the program. The move would bring in an estimated 6 million new contributors, who would bolster the retirement fund in the short run, until they themselves begin to qualify for benefits.

Begin moving toward limited use of the income tax to finance the Social Security program - possibly by diverting the hospital insurance portion of the payroll tax to pay for the system's retirement and disability programs, and then "reimbursing" the Medicare program with monies from the income tax.

Ullman also has hinted several time at adopting a European-style value added tax - a complex form of national sales tax that is levied at various stages of manufacture and ultimately passed on to consumers. Like the sales tax, the value-added tax is an efficient revenue-raiser. But it hits the poor the hardest.

Slowing the growth of benefits for future retirees. Under the law now in effect, benefits are pegged to an inflation adjustment scale designed to guarantee that benefit checks of future retirees will amount to the same proportion of their pre-retirement wages that today's pensioners are receiving.

But some analysts contend this ratio could be pared because workers wages will be much higher at the turn of the century, even after adjustments to account for inflation.

At the same time, there also are continuing pressures for added benefits. Penner points out that Congress still must deal with changing the pension laws on treatment of working spouses to give both marriage partners equal benefits. And there are calls to remove the cap on the amount of money retirees may earn.

"The problem is, all of these increases will cost money," he says. "The facts of life are that Congress probably is going to have to cut other benefits some in order to be able to afford new ones. But that isn't going to be an easy thing to decide."