IT'S TIME THAT we stopped all the foolish talk about how difficult it would be to balance the federal budget.

If we should ever adopt a constitutional amendment to that end, the deed could be done without any noticeable pain -- except perhaps to those who believe that editing the Founding Fathers would produce some wrenching fiscal changes.

The fact is that a quite legitimate and painless way not only to balance the budget but to create a multibillion-dollar surplus has been sitting under President Reagan's nose. All he has to do is flip through the authoritative works of David Stockman's Office of Management and Budget to an entry, for fiscal 1983, called "Special Analysis D."

"Special Analysis D" conveniently divides the federal budget into two categories, one for "current" outlays -- otherwise known as day- to-day operating expenses -- and another for "capital" programs with longer-term payoffs, such as those for highways and bridges.

The president will see immediately that by removing Stockman's "capital" budget of $155.3 billion, he can transform this year's estimated deficit of about $140 billion into a surplus of about $15 billion. Presto, Washington's first black ink in ages.

The notion of a separate capital budget is by no means unusual. The president should be exceedingly familiar with it, since he had one as governor of California. Indeed, as many as 45 states -- including most of those that have called for a constitutional convention on the federal balanced-budget idea -- keep their ledgers looking good this way.

In nearly all these states, capital spending is excluded from the regular budget. Capital programs are viewed not as expenses but as investments, and they are funded separately, largely through bonds or other borrowing devices. Without this accounting device, most states that have pointed piously to their own budgetary black ink would have been knee- deep in deficits for years.

Doing this at the national level as well might strike some as phony accounting designed to camouflage deficits, not reduce them; there certainly is some merit to this claim (as accountants for New York City in past decades would be the first to suggest). But the capital budget also has substantive merit.

There is a difference between money spent to yield future benefits and money laid out for current expenses. By making the distinction explicit, we could not only instantly balance the budget -- we could also focus the federal spending debate more properly on the relative need and rationale for spending in various areas.

For example, with bridges, highways, subways and dams decaying and cracking beneath our feet, massive federal spending to rebuild these structures will be required in the coming decades. Indiscriminate rhetoric about slashing federal spending does the public a great disservice, since it is clear that some areas will require -- and quite properly -- more, not less, federal capital.

Similarly, a balanced-budget drive that decimates federal research and development outlays could easily have the perverse effect of stunting our future technological growth, reducing or removing a major American advantage worldwide and shrinking our economic growth.

But let's leave all this weighty substance aside and focus on the psychological effect. A separate capital budget would remove from our shoulders the tremendous weight of pondering staggering deficits now and through the rest of the 1980s. It would free us from worry about how Congress could possibly cope with a constitutional commandment to balance the budget. We would simply redefine the meaning of budget. The capital budget is worth it for those reasons alone.

As for details, any two people might quibble over precisely which federal programs belong on the investment side of the ledger. But why not just take David Stockman's view on this?

OMB defines capital, or "investment- type," programs as those which "yield benefits in future years through the acquisition of physical or financial assets, or through expenditures for less tangible long-term benefits such as education. They include: the construction, rehabilitation and acquisition of physical assets; education, training, and vocational rehabilitation; research and development; international development; and financial investments such as loans."

Buying the Stockman formula (see the accompanying table for details), we can in one fell swoop create that $15 billion surplus, remove the need for a constitutional amendment, painlessly balance the budget if an amendment should be adopted, and end the balanced-budget clamor of Wall Street and the hinterland. I would sleep a lot more peacefully knowing that we had solved this nettlesome problem once and for all.