Middle-income families pay one-third more of their earnings in state and local taxes than do the richest Americans, a labor-backed research group said Monday.

The disparity is even worse for families in the bottom one-fifth of the income scale, said Citizens for Tax Justice. The poorest families see 81 percent more of their earnings swallowed up by state and local taxes than do the most affluent."The biggest problem is overreliance on regressive sales and excise taxes rather than on progressive, ability-to-pay income taxes," said Robert S. McIntyre, director of the group.

The findings were included in an analysis by Citizens for Tax Justice of the major taxes and who pays them in the 50 states and the District of Columbia.

The organization, which is supported by unions and religious and social action groups, has long advocated higher taxes on the wealthy and greater reliance on income taxes.

The study found that only Vermont and Delaware have tax systems that are even slightly progressive, meaning that they are based on ability to pay. The 10 states considered to have the least-fair taxes require middle-income families to pay up to three times as much of their earnings compared with the rich.

The eight states viewed as having the worst tax systems - South Dakota, Nevada, Texas, Florida, Washington, Tennessee, Wyoming and New Hampshire - have no broad personal income tax. Pennsylvania and Illinois, the other two states found to be most regressive in taxing, have flat, low-rate income taxes.

Washington has the highest taxes on the poor: 17.4 percent of their income, the report said.