TO NO ONE'S surprise, Congress has now extended for another five years the extremely popular program of low-interest guaranteed loans to college students. As the debates over government spending roar along, the student loan program is not a bad example of a multi-billion-dollar benefit to keep in mind. The reasons for its popularity aren't hard to grasp. No interest is charged on the loan while the student is in school. The interest rate, after the student leaves the classroom, will be 9 percent a year -- about half the commercial rate. Best of all, this fat benefit is not restricted to the group of people known in current political discourse as "them" (i.e., the poor), but is available to "us" (i.e., the people with average-and-upward incomes).

Why should anyone question this pleasant opportunity? After all, it's just a loan, and college costs have risen at such an astounding rate that only the richest can fail to feel the pinch. Don't we have a right, now and then, to do something nice for ourselves?

But it's not just a loan. There are costly federal subsidies required for the deferral of interest and the bargain rate. There is the inevitable and substantial cost of the defaulted loans. Beyond that, there are the costs -- subtler, but no less real -- associated with giving more of the control over our saving and purchasing decisions to the federal government, trading higher taxes for guaranteed benefits.

About half of the federal budget is now a gigantic insurance fund. Congress has sold you a policy -- the premium is in your tax bill -- and in return you are insured against a great many important needs. The policy includes an old-age pension, medical care, protection against loss of income and a great many other things including, in this case, money to finish college. Each of these things, taken by itself, is a good and decent provision. But all of them, taken together, are the reason that your taxes are going up so fast.

Clearly, many of these kinds of social insurance are essential to American ideas of economic justice. But the questions of degree are getting sharper. Are all of these programs equally needed? Do they all deserve rapid and continuous expansion?

A number of the more committed social democracies like Sweden are now beginning to reconsider certain of these commitments. They not only restrict individual citizens' spending choices, but also crimp incentives to work and to save. Social insurance is important. But it's also important to remember that, from time to time, the premiums come due.