HAPPY TAX DAY. To those who have succeeded in getting the wretched form filled out and in the mail, congratulations. To those who have not, you've got until midnight. In either case, you may have a few thoughts on the subject of Form 1040. Our own view is that, entirely apart from the amounts of money changing hands, the whole process of tax-paying is getting out of hand in its demands on citizens' time and patience.

Everybody agrees that there's something profoundly wrong when a large and growing proportion of the taxpayers no longer understand the basic rules or dare to fill out their own forms. The anomalies are striking. Mortgage interest is deductible, but rent is not. Insulation for your attic, or day care for your child, can mean a tax credit, but medical expenses are only a deduction. Dividends paid by a utility are deductible if reinvested in the utility's stock, for the utilities are a distressed industry. But dividends paid by the automobile companies are not deductible, although the automobile companies are also in distress. If you save for your retirement, the interest is not taxable. But if you save for your children's education, the interest is fully taxable. As every reader knows, the list of examples could be continued right to the bottom of this page, and all through the next one, and on right through the final page of the last section.

Many of these distinctions are absurd, and most are hardly worth the trouble either to the taxpayer or to the country. But they all have amazingly vigorous defenders. As you listen to the debates over them, you will repeatedly get the impression that these tax benefits are valued far beyond their economic worth. To their advocates they often seem to represent not only money but something more--a stamp of social and moral approval for the favored endeavor, whether it's installing solar heating, or drilling for oil, or distilling corn into gasohol.

Everybody knows that the personal income tax has become far too onerous and, on this date each spring, everybody says so bitterly and loudly. The ideal income tax would be a flat percentage of all income above an arbitrary threshold of, say $10,000 a year. It would be simple, quick and easy. As for fairness, it would be no less fair than the present tangle of exemptions, deductions and credits that are currently producing not equity but a widespread public cynicism and hostility. The flat tax is the obvious remedy. But, for all of the equally obvious reasons embedded deeply in American political traditions and folkways, the system continues to evolve rapidly in the opposite direction.