In passing a tax bill heavily weighted toward the upper-income brackets, the 95th Congress, heavily Democratic and liberal, has thrown down a challenge to Democrats and liberals: Do we or do we not want to use the tax laws to redistribute income?

Sen. George McGovern (D-S.D.) answers the question this way: "I cannot remember a Congress that has done less for the working people in this country."

McGovern objected to that portion of the energy program that raised prices for everybody's home heating and gasoline regardless of their ability to pay. But the main thrust of his criticism was directed at the 95th Congress's tax cut, which clearly benefited the country's millionaires a great deal more than it benefited the country's poor.

Nearly all of Jimmy Carter's tax-reform proposals were rejected. The big foreign tax breaks for the multinational corporations that the president wanted to stop were reaffirmed. So was the expense-account living that he tried to symbolize in his campaign against the "three martini lunch."

Moreover, the 95th Congress cut the capital-gains tax by more than $2 billion, a bonanza for those who make more than $50,000 per year and who therefore have something to sell. The low-bracket wage-earners who have nothing to sell will pay the bill.

Even on the strict withholding-tax basis, the tax is loaded for the relatively well-to-do. Is it fair to so apportion what the 95th Congress calls "tax relief"? Would it not be more fair if the $10,000 earner got a tax break of 40 percent? The figures would so suggest.

But it is worse than that. If you earn $20,000 to $30,000 per year, you get a tax cut of about 7 percent. If you earn $200,000 and over you also get a tax cut of about 7 percent. Is this what the progressive income tax was supposed to mean?

I suppose that there are theoretical communists who believe in absolute equality of income. I don't know any liberals who do. But can the values of democracy justify a system in which the poorest fifth of the population receives about 5 percent of the national income while the richest fifth receives about 41 percent?

And is there any movement to correct this gross disparity when the Congress passes a tax bill calculated to give that upper fifth an even more advantageous position?

We have, in fact, a situation of such disproportion that it may trouble us deeply in the event of the depression that some economists are predicting. So what do we do about it? We make it worse.

There is a "Let them eat cake" quality to the tax bill that defies explanation. The members of the 95th Congress are not aristocrats who are unwitting of the country's condition. They are, as I said, mostly Democrats, mostly liberal. Then how can they account for their tax bill?

They may have been listening to lobbyists. They were certainly not listening to the president.

"Gross tax inequities are being perpetuated," wrote Jimmy Carter in 1975. "Carefully contrived loopholes let the total burden shift more and more toward the average wage earner . . . When oil companies pay less than 5 percent on their earnings while employees of the company pay at least three times this rate, when many pay no taxes on income of more than $100,000 - then we need basic tax reform."

That's what he said. But "basic tax reform" is not what he got. He ought to veto the tax bill.