President Carter's income tax cut proposals would offset rising Social Security taxes for most families, but there is one group whose total tax load would rise substantially.
It is the small but highly influential minority of working couples who earn $40,000 a year or more.
The reason is that the Social Security tax increase would be much greater for these households than for most others.
New tables made public by the Treasury show that by 1979 the combination of the president's tax proposals and the higher Social Security taxes would raise the total tax burden for these couples between $333 and $1,467 over what they will have paid on their 1977 income.
One-earner families in the same brackets would also see their total tax burdens rise, but considerably less - between $221 and $1,029.
On the other hand, two-earner families in the $20,000-to-$30,000-a-year category would come out better than those in the same bracket with a single breadwinner.
These families would see their tax burdens lightened in 1979 by between $214 and $250, while those of one-earner families would change relatively little. The maximum the burden for one-earner families would rise would be $117.
While only about 16 percent of the nation's taxpayers are in the $20,000-a-year-or-over bracket, the proportion in the Washington metropolitan area is significantly higher. Estimates show that about one-third of the families here earn $25,000 or more a year.
But many of these families draw at least part of their income from federal government - and government employees would enjoy larger than average tax cuts under the Carter proposal. The reason is that they would receive the full reduction in income taxes even though they don't participate in the Social Security program and so wouldn't be hurt by the payroll tax rise.
For a family of four, these workers would enjoy tax relief in 1979 ranging from $258 to $322 - as much as $261 more in tax cuts than families where the breadwinners are employed by private firms. The gains would be the same for both one and two-earner families.
Figures complied by the congressional Joint Committee on Taxation show that, not counting in the effects of the scheduled Social Security tax increases, Carter's income-tax proposals would raise taxes for 2.8 million Americans - about 4 percent of the 64 million taxpayers who earn enough every year to incur tax liability.
Included among these would be high-income families with large numbers of dependents; families with moderately high medical expenses and taxpayers with unusually large deductions for state and local sales taxes.
These increases would come because of Carter's proposals to replace the present $750-a-dependent personal exemption with a tax credit of $240, and eliminate existing deductions for state and local sales taxes and all but catastrophic medical expenses.
The disparities in tax treatment of higher-income taxpayers could cause when the tax package goes to Congress. Despite their bent for providing proportionally larger cuts for lower-income families, the lawmakers are sensitive to concerns of middle-and upper-income taxpayers.
The Treasury did not include the table affecting two-earner families in the package it gave reporters over the weekend. Officials had planned to unveil it in a formal presentation to the House Ways and Means Committee later this month.