AS ALWAYS, too many of us will put off the annual exasperating business of paying our taxes until the last minute (which, if you really must know, is not until April 17 this year). Still, while people are digging out their records, squinting at instruction books, cursing or taking the whole thing to someone else for help, we'll offer you one of our 17 reasons for taking a second annoying look at the math required to complete your state or D.C. income-tax forms. Reason No. 1: If you are filing a Maryland or Virginia return, you're better off than the D.C. taxpayer - whose tax forms look like the federal ones but have the fewest similarities when it comes to itemizing deductions.

Why, you may now ask, can't that process be simplified by bringing the District income-tax law more into line with the federal code? If that were done, a taxpayer could work on his or her federal return first, then just transfer most of the totals to the District form. Exemptions, tax rates and a few deductions could still be different, but the calculations would be faster and easier. Indeed, for many people it might eliminate the middleman now needed to assist with the filing chores.

City offials can come up with their own 17 bureaucratic reasons for keeping thing complicated, none of which is likely to wash with the paying customers: a) the possibility that the city might lose a penny or so in the first year of a change, b) the possibility that certain deductions allowed by the federal government should be blessed as city policy or c) all the above minus 11.62 percent of Line D or half of your living room, whicever is greater.

It can't be all that bad, however, for a majority of the states (including Maryland and Virginia) now base their income taxes explicitly on all or most of the federal definitions and rules. Moreover, the city council has eliminated some of the make-work in the D.C. forms, theough a bill introduced two years ago by council member Polly Shackleton. Certain itemized deductions were adjusted to be treated by the city as they are by the Internal Revenue Service.

Nevertheless there are still some nuisance differences, such as the way deductions for contributions are treated.On the D.C. forms, deductions are limited to those for organizations that carry on a substantial part of their charitable or educational activities in the Distric. Thus, if you live somewhere near the District line and go to church in Montgomery or Prince George's counties, contributing to that church are't deductible. And political contributions are treated differently by IRS and the city. And the city doesn't allow the $100-per-taxpayers dividend wxclusion allowed by Uncle Sam.

And so on. For additional guidance, we recommend the series of articles by E.M Abramson that appeared in the Business and Finance section of this newspaper last month. (Back copies are available at the newspaper's front counter.) In the meantime, we urge the city council to enact the changes necessary to maximize conformity with the federal forms - both to please their constituents and to ease city hall's auditing burden.