Some information was inadvertently omitted from the two charts accompanying the story on personal income tax burdens that appeared in Sunday's Business and Finance section. The charts traced changes in marginal tax rates from 1960 to the present, and what would result from President Reagan's proposed tax cut, for four 1981 income levels. The income levels, $12,500, $25,000, $40,000 and $500,000, were omitted. Also, the marginal tax rates were expressed as percentages, not percent of change as indicated.

The rising burden of personal income tax is no joke to the millions of Americans still struggling with their 1980 returns -- which must be in the mail by midnight Wednesday -- nor for the many millions more who already have completed the chore.

The Reagan administration claims that increasing personal tax burdens, and particularly higher marginal rates, are to blame for a significant part of the nation's economic distress. And as soon as President Reagan is sufficiently recovered from the recent attempt on his life, he will lead a new charge to get Congress quickly to enact his proposed 30 percent cut in those marginal rates.

With the progressive income tax, blocks of income are taxed at steadily rising rates that now range from 14 percent to 70 percent. Reagan would lower the rates to the 10 percent to 50 percent range. With a progressive tax system, the first dollar of income is not taxed at the same rate as the last dollar. The marginal rate is the highest rate of tax on that last dollar of income.

When the Reagan tax package was offered in February, Treasury officials argued, "As rational human beings, we should all realize that if additional income isn't taxed away as much as it is now with high marginal rates, we will have more incentive to go out and earn more income. . . . Furthermore . . . most people will realize that it is more profitable to save a greater portion of after-tax income and invest it rather than to spend it immediately."

But no one in the administration has ever spelled out just how much marginal rates have risen. Nor has anyone described in detail what marginal rates will be in 1984 for certain income levels if they rose with inflation, pushing an individual up the progressive tax rate scale.

To shed some light on these issues, The Washington Post undertook a study of what has happened to marginal rates during the past two decades, as well as what would happen to them between now and 1984 if the Reagan tax cut were passed and his highly optimistic forecast of much lower inflation and much faster economic growth actually came to pass.

Actual tax liabilities, marginal rates and average rates -- that is, the total tax due as a percentage of total income -- is expressed for 22 different income levels. The income levels were expressed in terms of 1981 dollars. Income in earlier years was adjusted for inflation -- for instance, a $40,000 income this year is the equivalent of only $14,092 in 1960. The administration's inflation forecast was used to adjust income levels through 1984.

Given all the rhetoric about rising marginal tax rates, a surprising picture emerged as the actual tax burdens on this wide range of real income levels was traced beginning in 1960. Three principal conclusions can be drawn.

First, the results suggest that by historical standards, the nation is ready for a tax cut. Average rates, which most economists regard as a better measure of tax burdens than marginal rates, were as high or higher last year for all but a few married couples with two children as they were in 1963 or 1969, two years in which major tax-cutting legislation was passed. However, average rates for single individuals, who received a paticularly large tax cut in 1969, were still below their 1969 peak for all 22 income levels.

Second, there is little indication that the increases in marginal rates have been so pervasive and so sustained that they necessarily have had much to do with creating our current economic difficulties. Marginal rates for most taxpayers are only slightly higher than their average level from 1960 to 1979. But can very small changes in marginal rates provoke very large changes in economic behavior? No one in the administration has ever spelled out just how sensitive "rational human beings" are to changes in marginal rates. Does dropping a marginal rate from, say, 36 percent to 34 percent, make a great difference; or does 36 percent have to become 30 pecent or 26 percent or lower to make people sit up and take notice?

Third, whatever damage rising marginal and average tax rates may have done, the Reagan tax cut will do little to correct it. With inflation continuing, marginal rates in 1984 will be lower than they were in 1980 for most taxpayers, but not sharply lower except for those with the highest rates now.

Of course, the Reagan proposal would leave all taxpayers much better off in 1984 than if there were no cut at all. The question is whether in the process some fundamental change would be wrought by cuts only in marginal rates.

Even though Reagan wants to reduce all marginal rates proportionately, the actual results turn out to be capiricous once the impact of inflation, the vagaries of tax law and the irregular nature of the tax brackets come into play. In all the calculations, it was assumed the taxpayers used a standard deduction (or zero bracket amount) or itemized deductions equal to the actual average for the year in question, or 23 percent of income for 1979 and later years. Others items, such as residential energy tax credits, were ignored.

The Reagan plan calls for no increases in the size of the $1,000 personal exemption, whose value would be eroded by 35 percent from 1980 to 1984 according to the administration's inflation forecast. The so-called zero bracket amounts -- the equivalent of the former standard deductions -- are not to be increased either.

All in all, the Reagan plan produces some peculiar results. For example, married taxpayers with two dependents and incomes comparable to 1981 incomes of $22,500 and $40,000 would, in 1984, be paying exactly the same marginal rates as they did last year. With an income comparable to $27,500, $35,000 and $50,000, the rates would be cut only a single percentage point. Because the earned income credit for low-income families declines as income rises, the marginal rate on a $7,500 income would go up 15 percentage points!

Single taxpayers generally would get larger cuts in both average and marginal rates. But there, too, the results are not uniform. A taxpayer with an income comparable to $30,000 in 1981 would get only a 2 percentage point reduction in marginal rates between 1980 and 1984 and only 3 points off at $35,000. But at $40,000 the cut is 8 percentage points. But, again, at the same $40,000 income level the married couple with two dependents would get no marginal rate cut at all.

If cuts in marginal rates and only marginal rates can provide incentives for work, saving and investment, what should one make of these results? A couple earning $30,000 this year who has two kids and who just stays even with inflation will see their marginal rate drop by 5 percentage points, from 28 percent to 23 percent. But if they worked hard, saved their money and invested it so as to get their income up to $35,000, they would find their new marginal rate only 1 percentage point less than in 1980 for a comparable income. If they ignored the fact that marginal rates was only slightly lower than it was in 1980 and managed to move on to $40,000, they would find the rate identical to last year's rate.

A look backward over the last two decades is just as interesting as casting forward to 1984. Here are some of the things the study of marginal and average rates shows:

Marginal rates were only slightly higher in 1980 than the average for the 1960-79 period for taxpayers with income of less than $20,000, or roughly 60 percent of the total. Such taxpayers account for nearly 30 percent of reported income.

Similarly, married taxpayers at the top, the handful with incomes above $100,000, accounting for less than 5 percent of reported incomes, generally had a lower marginal rate in 1980 than in the 1960-79 period. Those lower rates stemmed from the cut in the top rate from 91 percent in 1963 to 70 percent in 1965. In addition, a maximum rate of 50 percent on earned income supposedly has been in effect since 1970, though the rate turns out to be higher for most taxpayers making the special calculation. Like those at the top, taxpayers with incomes below $10,000 also generally had a lower marginal rate last year than in prior years.

Married taxpayers with two children who had incomes between $20,000 and $30,000 and filed joint returns had marginal rates that averaged only 3 percentage points higher than their two-decade level. Single taxpayers in the same income range had marginal rates that averaged 4.6 percentage points higher. About 25 percent of all taxpayers have income in this range, and they have about 30 percent of reported income.

The rates for the remaining 15 percent or so of taxpayers, whose incomes run from $30,000 to $100,000 and who had about 35 percent of all income, were higher by from 3.3 to 11.2 percentage points. The average marginal rate for this group in 1980 was 41.1 percent; the average for 1960-79 was 34 percent.

Thus, changes in the marginal rates for different taxpayers, in the past and in the future, fall all over the lot. Some are down relative to prior years and some are up only slightly. Still, for the upper 15 percent of taxpayers, except those at the very top, rates are higher.

Clearly, the Reagan proposal would lower marginal rates for many in that hard-hit 15 percent. But will taxpayers know what has happened to their particular marginal rate? The administration's theory assumes they will. Yet the vast majority of taxpayes this year are simply finding the amount of tax they owe for 1980 from tax tables in the Form 1040 instructions and never have to look at the tax rate schedules. Nowhere in those tables, which cover taxable incomes to more than $440,000, is there even a hint of a marginal rate.

Even if a taxpayer knows his rate now, how quickly would he learn it has been changed and by how much? The administration's rosy economic forecast clearly assumes that flow of information will be swift indeed.