THE ELDERLY are numerous and vote, and the shameless political pandering to them goes on. The administration has now let it be known that it will not oppose a cost-of-living increase for Social Security recipients this year, even if, as expected, the inflation rate is too low to trigger an increase under the law. Congress has already indicated it will simply change the law; the administration will go along. "We've had a significant savings from the lowering of inflation, and people on Social Security should have some sharing of that," budget director James Miller said in a speech the other day.

That's absolutely backward, a non sequitur, a bowl of verbal mush meant to suggest that there's some equitable reason for doing a thing that they're going to do anyway, not out of a sense of equity but out of fear, and not even so much fear of the old folks as of one another. With cause, each party senses that if it even hesitates on Social Security the other will go for the throat and demagogue on the issue, the more so as the elderly each year become a larger share of the population. It's wrong, most members know it, and they're too scared to care.

Congress indexed Social Security benefits in 1972. The irony is that the step was taken in part to preserve the members from temptation, to break the earthy habit of voting costly increases in election years. The rule was that beneficiaries would be paid the inflation rate if it exceeded 3 percent. If not, as is likely this year, they wouldn't lose it; it would just count toward the next year's increase.

Defenders say that in the long run it will cost the system more money to give no increase this year and a large one next. Maybe. For the short run, there are good reasons to let this already generous law operate as written. The deficit is the most obvious. If benefits aren't increased, neither the wage base against which the Social Security tax is levied nor the premium for so-called Part B insurance under Medicare (the part that pays doctor as opposed to hospital bills) will go up, either. The government will still save several billion dollars in fiscal 1987. That's when it badly needs such savings.

There's also an argument as to indexation. For most of the Reagan administration we've been persuasively told that too much of the budget is indexed, tied too closely to the consumer price index. This would tie a fifth of the budget even closer.

But none of this matters. If you want a clear vision of what is happening here, ask yourself what it would be like if the issue were a cost-of-living increase for welfare recipients instead of the seventh of the population on Social Security. Welfare recipients are poorer. Would it make any difference? Would we be hearing the same unctuous speeches about transferring out of the Treasury the blessings of low inflation? You know the answer.