A woman who retired from the government last year and got a $60,000 lump- sum pension check will pay about $36,000 to the federal and District governments because of complex, last-minute changes Congress made in tax rules covering retirement income.

Although this case is extreme, it illustrates the tax bite that faces almost every federal, state or local government worker retiring in the future who takes a lump- sum pension payment. That is, unless a group of unhappy retirees is successful in a lawsuit it is preparing to take to the U.S. Claims Court.

Last year, 48,000 federal retirees took lump-sum pension payments by agreeing to a lifetime reduction in their annuities. The benefits were worth $1 billion, but at least $300 million of it has gone back to the government, or will go back to it, in taxes.

This is the situation: After retiring last year, the D.C. resident was contacted by the Office of Personnel Management. It advised her of the lump-sum option, which represents an amount equal to all the money she paid into the retirement fund while working. Congress originally intended that the payments, which had been previously taxed as income, would be tax free. But the Tax Reform Act changed that.

It said that a substantial portion of any lump-sum payment -- anywhere from 85 to 95 percent -- would be taxable. The law said that this was the amount attributed to the government's total share of future retirement payments.

The woman asked for more time to decide, because Congress and the Internal Revenue Service hadn't clarified the new rules. But OPM advised her that by law she had to make a decision within 30 days of being contacted. She took the payment, which was about $60,000.

Later, however, IRS rules issued said that a substantial portion of the lump sum would be taxed at the 38 1/2 percent rate for 1987 because of her relatively high income. Also, she was hit with a special 10 percent early retirement tax Congress recently added to lump-sum benefits of federal workers who retire before age 55 and nonfederal workers who retire before age 59 1/2.

Those taxes plus her 12 percent liability to the District meant a tax bite of about $36,000, cutting her $60,000 lump-sum payment to about $24,000.

The lawsuit challenging the lump-sum pension tax is being pushed by 520 recent federal retirees. Each has signed on and paid $500 to fight the case in court. Washington attorney Tom O'Rourke will handle the case, which is being coordinated by the Senior Executive Association here. SEA represents many workers who, because of their high salaries and potential lump-sum payments, have the most to lose.

Last Saturday on WNTR radio, O'Rourke said that the case could take from one to five years. He said it is possible that if the case is won it could benefit only those who are plantiffs in the lawsuit. For more information on the case, send a self-addressed envelope (with 39 cents postage) to SEA at P.O. Box 7610, Ben Franklin Station, Washington, D.C. 20044.