A four-member family earning $31,000 a year pays three times as much of its income in state sales and excise taxes as does one making over $612,000, a private study reported today. The share of earnings soaked up by those taxes is almost five times as large for the poorest families _ those making less than $8,600 _ as it is for the richest, according to a report by Citizens for Tax Justice. This happens because the taxes are applied at a flat rate regardless of income. In 23 states, the disparity is even worse than the national average. The poor in South Dakota and Mississippi pay about seven times as much of their earnings in sales and excise taxes as do the rich; in Tennessee, Alabama and Louisiana, almost six times as much. The study focused on general sales taxes and on excise taxes, chiefly those on gasoline and tobacco. It concluded that: _The poorest 20 percent of four-member families, averaging income of $8,581, paid 5.4 percent of their earnings in sales and excise taxes last year. _The second one-fifth, averaging $20,535, paid 3.9 percent. _The third, averaging $31,497, paid 3.3 percent. _The fourth, averaging $44,910, paid 2.9 percent. _The highest-earning one-fifth, averaging $66,912, paid 2.5 percent. _The top-earning 5 percent, averaging $187,316, paid 1.6 percent. _Four-member families averaging $612,122 a year _ the richest 0.7 percent of Americans _ paid 1.1 percent of their incomes for sales and excise taxes. Citizens for Tax Justice is a Washington-based research organization that is financed by organized labor and several liberal social groups. The organization considers income taxes more equitable than consumption taxes, including excise and sales taxes. Income taxes generally take a bigger bite of each dollar as income rises and, thus, fall more heavily on upper-income Americans. ``By relying on nickel-and-dime sales taxes, state governments across the country have quietly heaped an onerous burden on their poorest citizens,'' Robert S. McIntyre, director of Citizens for Tax Justice, said in releasing the study. ``The less you make, the worse you do _ especially in states with heavy taxes on food, utilities, tobacco and fuels.'' The ultimate solution, he said, is for states to rely less on sales taxes and more on income taxes. In the meantime, McIntyre added, sales taxes can be made less onerous by extending rebates to the poor and applying the levies disproportionately to services that are generally used by the well-to-do, such as club memberships and home-improvement services. The study concluded that the 10 states with relatively low tax burdens on the poor have considerably more money available for public services than do the 10 whose sales taxes on the poor are highest. ``Taxing the poor heavily is both cruel and inefficient,'' said McIntyre. ``It doesn't produce much in the way of revenues because the poor don't make very much money.'' Sixteen states still fully tax food; over 22 percent of all food purchases in the United States are taxed. In fact, the study found, the 10 states with the most onerous sales taxes on the poor all tax food. They are: Alabama, Mississippi, Georgia, North Carolina, South Carolina, Arkansas, Tennessee, South Dakota, Virginia and Hawaii. The poor spend 6.2 percent of income on electrical bills, more than double the rate of the middle-income family. But that middle-income family pays three times as big a share for electricity as do the rich, the study found. The portion of the $600,000-a-year family's income spent for tax on take-home beer is only 15 percent of the $8,600 family's share. On cigarettes, the upper-income family's share is 1 percent of the low-income family's; on gasoline, 4 percent; on fresh flowers, 98 percent; on legal fees, 100 percent; jewelry, 259 percent; wine for home consumption, 324 percent, and out-of-town lodging, 613 percent. The study found that only six states have set up a system of tax credits to reduce the sales-tax burden on the poor. In only one state, New Mexico, would the credit offset as much as half the burden. The six states and the theoretical reduction for the poor, if all the poor applied for the credit: New Mexico, 64 percent; Kansas, 35 percent; Vermont, 26 percent; Idaho, 22 percent; Hawaii, 17 percent, and North Carolina, 7 percent.