Bush administration budget negotiators want to kill a proposal that would let federal workers with life-threatening diseases such as cancer, AIDS or serious heart problems get an immediate 100 percent pension payment when they retire.

A stunned supporter of the benefit for terminally ill retirees dubbed the administration opposition "necrophilanthropy" -- an attempt to balance the budget on the backs of dead federal retirees.

Individuals diagnosed as having a short time to live now can retire and get their lump-sum payment, which averages $32,000, in a single check. Some use it to cover medical expenses, pay bills or leave a nest egg for their families.

Other federal retirees get the lump sum in two equal payments: the first shortly after retiring, the second one year from the date of retirement.

About 80 percent of all retirees take the two-stage payments, although they are taxable and reduce lifetime pension benefits.

The payments equal the amount of money -- 7 percent of salary -- the retiree contributed to the pension plan while working.

For long-service, higher-paid employees the payments can exceed $90,000.

Budget negotiators tentatively agreed to eliminate the lump-sum benefit in most instances.

The House Post Office and Civil Service Committee wants to extend the option until Nov. 30. Congressional negotiators assumed that the 100 percent payment for critically ill retirees would be continued even if the lump-sum option is eliminated for other employees.

The Office of Management and Budget has taken the position that keeping the option for the terminally ill "undermines the actuarial balance of the retirement program."

In fact, relatively few retirees have qualified for the 100 percent payment since the option was first offered in 1987.

Rep. William D. Ford (D-Mich.), chairman of the Post Office and Civil Service Committee, said: "Common decency dictates that a terminally ill retiree should have access to the lump sum to lend some peace of mind. When the life and death of federal retirees is relegated to an exercise in bookkeeping, the public policy debate has exceeded the bounds of reason."

The budget conferees are looking at extending the lump-sum option for one year (until Nov. 30, 1991) for federal workers called to military duty because of Operation Desert Shield and Defense Department civilians who were asked not to retire because of the Persian Gulf crisis. Adoption Benefit

Federal workers would be able to use sick leave for activities relating to the adoption of a child under a provision in the House Treasury-Postal Service Appropriations bill.

The measure, sponsored by Rep. Frank R. Wolf (R-Va.) would give adoptive parents the same right to use sick leave as biological parents who can use sick leave for prenatal doctor visits.