$2.6 trillion, a sum almost beyond comprehension. And giant yearly deficits, $155 billion in fiscal 1988, are adding to it. The costs of this debt are enormous, more than $200 billion in interest payments last year, a figure that makes it extremely difficult to balance the budget.

As bad as these numbers are, they do not represent the whole truth. In reality, the picture is much worse. By using bookkeeping that calculates borrowed money from federal trust funds as "income" and does not count it as "debt" that must be repaid someday, the federal government is playing games that could lead to financial disaster in the next 30 years.Here's how it works:

Fueled by the "baby-boom" generation, the Social Security fund, for example, has more money coming in than it is paying out. This surplus, by law, must be invested in U.S. government bonds. This invested money is then used in the federal budget and is counted as ordinary income.

As a result, the so-called "surplus" ceases to exist. It is simply spent along with other federal tax income for the year.

In 1989, some $116 billion in trust fund surpluses will be pumped into the federal budget. The budget deficit is estimated at $148 billion for the fiscal year - but the real deficit must also include that trust fund money, an actual deficit of $264 billion.

Unfortunately, the Social Security Trust Fund is going to need its money back, starting in the second decade of the next century as the baby-boomers begin to reach retirement age.

As the Utah Foundation pointed out in a study released this week, that will be a double blow to the federal budget. First, the surpluses will no longer be available as income. Worse, the hundreds of billions already spent will have to be repaid to keep Social Security afloat.

If today's problems of trying to balance the budget are discouraging - despite using all the surpluses from Social Security funds and other trust funds - what will Congress do when the crunch comes? The hidden debt will suddenly become very obvious as the money runs out.

Observers have called this failure to acknowledge the payback of the trust funds a "grand deception." A deception it certainly is, but grand it is not. By pretending that the hidden deficit isn't there, Congress is simply postponing the drafting of plans and programs to deal with it. And that delay itself is only going to make the problem worse.