At first, I didn't want to admit it. I tried to keep quiet about the new spreadsheet model I've been working with. It seemed so -- well, so obsessive to admit that I had set up a speadsheet incorporating all the major tax reform plans floating around Washington. Of course, I've had great fun with it; every time somebody comes up with a new tax twist, I load in the spreadsheet and find out instantly how the proposed change would affect my income tax bill. But it seemed so obsessive.

Then I discovered that a lot of other people, too -- particularly my friends of the Yuppie persuasion -- are seriously interested in the tax reform effort now moving toward almost certain passage in Congress. Among Yuppies, in fact, tax reform has become a topic of conversation almost as common as mortgage rates and outrageously overpriced new brands of imported mustard. So I shared my tax reform spreadsheet with some friends; they, too, became hooked.

Now I'm going to try to pass this obsession on to you -- by explaining how to set up a simple model on your personal computer spreadsheet (Lotus, Multiplan, Excel, or any other) to keep track of all the proposed tax reform plans and calculate how much each plan will save, or cost, you next April 15.

The comparative tax reform spreadsheet is easy to set up: It's just a series of columns across the screen, with each representing a different tax plan. You'll want to use the first column of your spreadsheet to label each line: "Interest," "Dividends," "Moving Expenses," etc.

The second column should replicate, in tabular form, all the information reported on your 1985 income tax return. That's the base line for comparison. Then you create a series of additional columns representing the various tax reform plans. Mine has separate columns for the plan President Reagan sent to Congress, the House Ways and Means Committee bill, and the bill now working its way through the Senate. I'll eventually add another column for the House-Senate conference committee bill.

The horizontal rows of my spreadsheet each represent a line on Form 1040. You will want, for example, a separate row for each type of income reported in the "Income" section of the 1040: "wages," "interest," "dividends," "tax refunds," "alimony received," and so forth. In this section of the spreadsheet, your entries will be the same across almost all the columns, because the tax reform plans generally treat income the same way current law does.

But where there's a difference, you factor it right into your spreadsheet. For example, the Senate tax plan would eliminate the existing $200 exclusion ($100 for single filers) of dividend income; that means my dividend income would be $200 higher under the Senate plan. On my spreadsheet, the entry for dividend income on my 1985 return is in cell C9; when I typed in the Senate tax plan, accordingly, I just entered the formula "C9+200."

Moving on through Form 1040, I have rows of my spreadsheet for each of the allowed Adjustments to Income: moving expense, employee business expense, etc. Several of these adjustments are changed in the tax reform plans. For example, the Senate plan would eliminate the "dual-earner" adjustment. So I just typed in "0" for the "dual-earner" cell in the column representing the Senate plan.

I then told the spreadsheet to find the total of my adjustments and subtract it from the total of my income entries -- that is, to calculate my "adjusted gross income."

Next you set up a series of rows for itemized deductions, taking care to reflect changing treatment of existing deductions in the various reform plans. The cell I like best on the whole spreadsheet is the one that calculates the personal exemption; for those of us with several dependents, the near-doubling of that exemption in the reform proposals represents a big tax savings. The spreadsheet subtracts total deductions and exemptions from adjusted gross income to arrive at "taxable income."

The last block of the spreadsheet computes the tax. This is a snap, because there are so few different tax rates under the reform plans it is easy to set up a spreadsheet formula to determine which rate applies in your case and figure your tax. The spreadsheet then calculates various credits and surcharges and finally comes up (on line 47 of my model; yours could be shorter or longer, depending on the types of income and deductions you have) with the amount of tax due. I set up mine so that the figure blinks green if it's lower than my current tax bill, and red if the "reform" tax is higher than what I'm paying now.

I found that a computer spreadsheet, with its myriad formulas and functions, was a perfect tool for quick calculation of the impact of potential tax changes. I built my spreadsheet by reading various newspaper reports on the tax bill; most valuable was the worksheet put together by Alan Murray in the May 14, 1986, Wall Street Journal.

I spent about an hour, in all, setting up this tax reform spreadsheet. I refuse to admit how many hours since then I've spent playing around with this intriguing computer model.