The design of a pension system to cover all government workers hired since 1984 is still being debated by congressional staff members. The main stumbling block to the program, which is supposed to be in place by June, is $2 billion -- the annual cost difference in bills approved by the Senate and House.

Once aides from the Senate Governmental Affairs and House Post Office-Civil Service committees have reached a possible compromise, a joint Senate-House conference committee is expected to give quick approval to the program, which initially will cover 300,000 workers.

Each bill would base future pension benefits on a combination of Social Security, civil service retirement and earnings from a tax-deferred investment plan. The Senate version would cost the government an estimated 21.8 percent of payroll.

The House version is more like the current system in that it permits retirement at age 55 (after 30 years of service) and provides fully indexed cost-of-living raises for retirees. It would cost about 25.3 percent of payroll. The current system, which would be retained for employes hired before 1984, costs about 25 percent of payroll.

The Senate would give pre-1984 hires the option of coming into any plan set up for new workers. The House bill would let them invest in part of the thrift plan, but otherwise they would remain under the current program.