Is yours a two-income family? Are you a working wife with small children? Self-employed? Working for the government or for a private company with a pension plan? A homeowner moving up to a more expensive home? A 55-year-old thinking of selling your home? A high-income investor? An older person with a substantial estate?

If you fit into any one (or more) of these categories, Uncle Sam has a present for you somewhere in the tax bill the president signed into law earlier this month.

In addition to the overall tax reduction that applies to all taxpayers, the Economic Recovery Tax Act of 1981 is loaded with goodies. The new tax rules will benefit all of the above groups plus some others I haven't mentioned.

Of course the reference to "goodies" applies only to the direct and immediate impact on the special interest groups involved. It will be many moons before we can gauge the overall effect of the new tax law (and companion budget reductions) on the national economy.

For the next few weeks, Your Balance Sheet will take a look at how the most significant changes in the rules will affect us. Let's start with the cut in individual tax rates, reputed to be the largest "people's" tax cut ever enacted.

The popular understanding of the indivial tax cuts is a 5 percent cut on Oct. 1, 1981, followed by 10 percent on July 1, 1982, and another 10 percent on July 1, 1983, for a total of 25 percent in all.

In fact, the total comes slightly more than 23 percent, because the 10 percent figures are applied to the original (1981) rates. And because they take effect in mid-year, the actual reductions for the various tax years will be different.

The neat precision implied by the numbers and dates refers to withholding rates, which will in fact be adjusted by those percentages for the first wage payments made after the effective dates.

But your actual tax liability will be calculated in accordance with new tax schedules included in the law. Your individual decrease in tax may vary up or down from the exact percentage, depending on where your taxable income happens to fall with regard to the upper and lower limits of the applicable tax bracket.

It is important to understand that your 1981 tax bill will be reduced not by 5 percent but 1 1/4 percent. That's because the 5 percent reduction applies only to the last three months (fourth quarter) of the year.

There would be horrendous administrative problems associated with any attempt to segregate "pre" with "post" Oct. 1 income. So the law simply provides for a reduction of total 1981 tax equal to one-quarter of the 5 percent -- or 1 1/4 percent.

If you use the tax tables (which for 1981 will go up to $50,000), you won't have to do any arithmetic; the reduction will be reflected in the table. Those whose taxable income is over $50,000 will make a one-step calculation on a work sheet to be provided in your 1981 tax package.

What does all this mean in terms of real dollars? Well, in 1980 a family with $30,000 in taxable income -- that's adjusted gross income minus deductions and personal exemptions -- would have had a tax liability, before credits or taxes, of $6,238. A family with the same income in 1981 will be looking at a tax of $6,160, a saving of $78. For 1982 the figure will drop to $5,608, for an additional $553 saving. For 1983 the tax will fall another $543 to $5,064. And finally, the tax liability for 1984 will be $4,818 -- $246 less than the 1983 tax bill and a substantial $1,420, or 22.76 percent, less than the original 1980 tax.

For a single taxpayer with $20,000 in taxable income, here are the comparable fighures: 1980: $4,177; 1981: $4,125; 1982: $3,752; 1983: $3,369; and 1984: $3,205. Total reduction from 1980 to 1984 thus comes to $972, or 23.27 percent.

As you can see, the dollar amount of tax savings realized depends on the amount of taxable income involved. Since the reductions result from an across-the-board percentage cut, taxpayers with higher incomes will realize higher dollar savings than lower-income taxpayers.

Of course, the figures shown account only for the tax savings resulting from the cut in tax rates. Other elements of the omnibus law -- the easing of the marriage tax penalty, for instance -- may result in even greater savings. These elements will be discussed in future columns.