The membership of Congress is almost certainly smarter and better educated today than it was a decade ago. The investment in education that began with the GI Bill and continued with Sputnik and federal aid to higher education -- to say nothing of the increasing competitiveness of electoral politics -- has had a marked effect in reducing the number of hacks in the House and Senate.

How, then, is one to explain the extraordinary inability of Congress to extract the lessons of experience in one area and apply them to other, related questions?

This conundrum has been gnawing at me ever since the Senate decided, in a rather offhand way, to throw into the tax bill a provision that would index future tax rates and deductions for inflation, starting in 1985, when the last of the scheduled Reagan-suggested cuts go into effect.

The political appeal of indexing is obvious. It ends bracket creep -- the unlegislated increase in your tax burden that comes when a cost-of-living pay raise moves you into a higher bracket. It ends the situation, in the words of Sen. Dave Durenberger, one of its proponents, where the "government, one of the primary causes of inflation, is also the main beneficiary of inflation."

Hooray.

But indexing -- especially when mandated four years in advance by people who can have no real idea what the economic climate will be -- is also the most hazardous form of revenue-roulette. It is a classic example of the Congress of 1981 hogtying and hampering the reasoned choice of the Congress that will be sitting in 1985.

Now, the discouraging thing is that if anyone ought to know that fact, it is the 57 senators who voted for indexing last week and the 218 representatives who have signed onas co-sponsors of a similar provision in the House.

Why should they know it? Because much of the agony they have been going through this year on the budget and reconciliation bills is the direct by-product of their predecessors' past embrace of indexing for Social Security, government and military pensions and a variety of other programs.

The folks who indexed those benefits were operating off what they considered a fine ringing principle. If Durenberger and Sens. Bob Dole and Bill Armstrong can see the wickedness of government "profiting" from inflation, their worthy predecessors in the 1970s could see that it was equally iniquitous to make retirees the victims of inflation.

When then-senator Frank Church put the cost-of-living indexing for Social Security into the law in 1972, the principle of equity seemed so obvious that it passed 82-4. What 82 senators could not foresee was that indexing would become so expensive within a decade that it could threaten the system with bankruptcy and could threaten the system with bankruptcy and could force Congress to such desperate expedients as eliminating the minimum Social Security benefits for a couple million 70- and 80-year-olds living on the ragged edge of poverty.

Ah, but the sponsors of tax-indexing say their provision is different, because it affects revenues, not expenditures. It is not. The principle, and the mischief, are identical. In both cases, the lawmakers of one era are telling a selected group of citizens that for all times, under all circumstances, they will be protected against inflation.

It is a double folly.Inflation is not a scourge that affects particular groups.It clobbers everybody, and it can be cured only when everyone understands that discipline and sacrifice are involved. To "index" anyone -- taxpayer or beneficiary -- fully against the impact of inflation is to reduce the odds that everyone will see the need for joint action against the common enemy.

Second, it is demonstrably dangerous to lock the government into a long-term fiscal policy that restricts future room for maneuver. We are not talking about trivial sums. The Congressional Budget Office estimates that in its first two years, tax-indexing would cost the government $50 billion. No one now sitting in Congress can possibly know whether those $50 billion will be needed to balance the budget in 1986 or whether returning them to the taxpayers in that year will stimulate a lagging economy or just feed the fires of inflation.

What we do know is that this Congress has yet to bite the bullet and reduce the major items of indexed benefits it inherited. Yet it seems blithely ready to forge for its successors a new set of fiscal handcuffs called tax-indexing.

A government in which benefits are indexed to rise with inflation while taxes are indexed to resist inflation would be a government on the way to bankruptcy, of course.

It boggles the mind that these smart folks we got in Congress now can't see that for themselves. Maybe we need to send them to summer school.