The Reagan Administration may suggest that federal workers put a little more into their own retirement fund next year.

The bigger paycheck bite is one of a number of personnel reforms being considered to shore up a workers' retirement fund that has been sustained in recent years by mushrooming contributions from the federal government.

Government workers now pay7 percent of gross salary into the fund. Retirement benefits are based on length of service and the employe's highest average salary during a three-year period.

For their contributions, employes retiring after 20 years can expect a beginning monthly annuity payment of just over 36 percent of their high three-year salary average.

A 30-year civil servant would get 56.25 percent of salary at retirement, and someone who stuck it out for 42 years could get 80 percent of pay. Annuities are adjusted each year to keep pace with living costs.

The next raise is due in April. Retirees who are under 62 will get slightly less than a full cost-of-living catch-up.

Federal annuities are taxed. Social Security benefits, generally much lower, are not taxed as of now.

Most American workers, except federal employes, pay 6.7 percent of salary (on amounts up to $35,700 annually) into the Social Security fund.

Government employes are not covered by Social Security. But, starting next month they will have to pay the Medicare portion(1.3 percent) of the Social Security tax.

One proposal being considered by administration planners would require federal and postal workers to pay 9 percent of salary into the retirement fund. That, or any other increase, would be in addition to the new Medicare tax.

Although the Civil Service retirement fund is sound, it would be in much better shape if Congress had made regular, legally scheduled contributions into the fund. Congress paid nothing into it for many years, even though legislators liberalized retirement rules to make it possible for more people to retire sooner.

These early retirees had the advantage of paying into the fund for a shorter time, while drawing benefits longer.

These early retirements, combined with automatic inflationary cost-of-living increases in employes' benefits and a drop in the number of U.S. workers (which means fewer people paying into the fund), are responsible for the fund's rocky future.

The Office of Personnel Management says that the civil service fund took in $6.7 billion in 1971 and paid out $3.7 billion. Income included $3.2 billion from agencies and$2.1 billion from workers. The rest was interest paid to the fund.

Ten years later, OPM says, payout had jumped to $17.8 billion and income had risen to $28.5 billion.

But a bigger chunk, $18.2 billion, came from the government while only $4 billion was contributed directly by employes. Interest payments totaled $6.3 billion.

Although workers make 7 percent contributions on gross salary, the average government employe gets back as an annuity within 18 months of retirement all of the money that he or she had contributed to the fund.

Social Security recipients recover their contributions even faster, because for many years the Social Security tax was lower -- around2 percent -- while benefits were being increased consistently by Congress.

A variety of retirement reforms, including raising the minimum age for standard retirement from 55 to 63, are under consideration.

Administration officials say that nothing has been decided yet, but that the president's new budget due out next month could contain some interesting recommendations.