IN ITS SCRAMBLE for revenue, Congress could usefully go back to last summer's tax cut and take another look at its provisions for business depreciation. The case for those huge depreciation benefits becomes increasingly hollow with the passage of time. Just about everybody realizes that the budget deficit is too big, and just about everybody--with the interesting exception of President Reagan--acknowledges that some of the future stages of the tax cuts are going to have to be cancelled. But why limit the discussion to the personal income tax?

Those depreciation schedules are already much too rich, and the present law would accelerate them again after 1984. For several categories of assets, the tax rates are already negative--meaning that the tax benefits add up to more than the cost of the equipment, and the U.S. Treasury is subsidizing the purchase. That subsidy is largest in respect to depreciation of cars and trucks, another example of the congressional inclination to keep bailing where it can be done inconspicuously.

But some of the examples fail even the test of a rational policy of corporate welfare. Mining equipment is also subsidized, and the mining industry is not an example of poverty these days. Under the new law, the effective tax rate on petroleum refining equipment is 1.1 percent, while on food processing equipment it's 20 percent and on the utilities' generators, 30 percent. The figures, incidentally, are published by the president's Council of Economic Advisers. Why such large disparities? No reason, except that in the disheveled and confused circumstances in which the bill was drafted, the fattest breaks went, as usual, to the industries with the biggest lobbies.

In addition to being grossly unfair to many industries, this depreciation formula is also ineffectual. The original reason for it, as you probably remember, was the great and urgent need to encourage business investment. As it turns out, business investment was flat last year and, according to both the Commerce Department and the leading private forecaster, it seems likely to fall this year.

One explanation is the recession. But the tax cut was supposed to fend off the recession. Another explanation is that the tax program hasn't yet had time to work. But all the depreciation provisions were retroactive to the beginning of last year.

Congress did its job badly last year, and the whole depreciation section of the law needs fundamental revision. A better law would eliminate the inequities among industries, and end the hidden subsidies. At a time when some of the personal tax cuts are going to have to be revoked, it would also reduce the disproportionate largess here for corporate taxpayers.