The most menacing threat to Social Security is not that it will run out of money two or three decades hence, but that members of Congress will use the current talk of reform to advance political agendas only tangentially related to protecting the retirement system. That is only one reason to make “incremental” the watchword for the coming debate.

The Social Security system is not in trouble in the sense that with one false move it will fall off a cliff. It is in trouble in the sense that the cliff is 10 miles away and the nation is driving toward it. Plenty of time and plenty of reason to turn, but not with one mighty tug on the wheel. A simple easing off the current path will do quite well, allowing the country to keep Social Security healthy for many more years.

Already, President Clinton and congressional Republicans are playing “After you, Alphonse,” each goading the other to present a reform plan first so the other can knock it down. That is unfortunate because, as both sides agree, the time is short for coming to agreement on the problem — meaning that they need to act while the nation is running a budget surplus and before the next presidential election campaign begins in full, next summer.

The reason for acting is simple: Given the level of money paid out, increased life expectancies and a diminishing number of wage earners in the first part of the next century, the Social Security payroll tax by 2013 no longer will be sufficient to cover benefits. By 2021, the interest from the Social Security Trust Fund won’t be enough to help cover benefits, and by 2032 the principal in the trust fund will have been used up.

Of the dozen or so reform options — raising the age to qualify for benefits, letting individuals invest the money privately, lowering benefits, increasing the payroll tax, increasing the wage base, etc. — three are particularly attractive because they deal with the problem cautiously, respecting the fact that the system has been one of the world’s most successful programs for wiping out poverty.

Let increases in Social Security payments better reflect inflation (instead of tracking the Consumer Price Index), increase the taxable wage from $82,800 to $97,500 by 2002, as suggested by Sen. Daniel Patrick Moynihan, and allow some cautious, long-term purchases of stock by the government to increase interest yields. This last proposal is not simple and would require an independent board to oversee, but could contribute to keeping the system solvent.

Some have suggested giving individuals part of the money to invest in higher yielding stocks than the Treasury bills the system currently buys. That has wide appeal, particularly among politicians who prefer the government not be involved at all in retirement, but it defeats the efficiencies built into Social Security investments: Would every single would-be recipient have to pay a brokerage fee for these small accounts?

Raising the age, as has also been suggested, similarly is troublesome because it shifts the problem entirely into the future, long after the current Congress retires. One of the original purposes of the Social Security system — ecouraging older workers to retire to make room for younger ones — will still stand in a recession and, in any event, the public has in no way offered to delay their retirements until age 72 or 75, no matter what the new life expectancies.

The debate over Social Security will begin in earnest this winter. When it does, be especially wary of members of Congress who propose massive changes to what amounts to a problem that will remain small — if Washington acts soon.