There is a good chance that Congress will act to preserve a generous investment option for top-paid federal workers that allows them to put up to 15 percent of their salaries into a tax-deferred savings plan.

Currently, federal employes who are covered by, or who switch to the new Federal Employes Retirement System (FERS), can shelter up to 10 percent of their pay (up to $7,000 a year) by putting it into the new thrift savings program. Workers under FERS who invest 5 percent or more of their own money also get a 5 percent tax-deferred contribution to their account from Uncle Sam. But the amount upper-income workers ($50,000-a-year and above) can contribute depends on the percentage of salary lower-income employes contribute.

Most government workers hired since the start of 1984 are automatically covered by the FERS pension plan. The two million federal workers hired before 1984 are now under the old civil service retirement system, which lets workers invest only half as much and does not provide any matching contributions from the government. Workers covered by the old retirement plan have until Dec. 31 to switch into FERS and take advantage of the more generous savings plan.

Many upper-income federal workers are delaying a switch to FERS because they don't know if they will be able to contribute 10 percent of pay to the thrift plan in the future because of the so-called antidiscrimination rule. That rule, which covers all 401 (k) tax-deferred savings programs, limits the percent of pay upper-income workers can invest to no more than 2 percent above the average percentage of income that all lower-income workers invest.

The antidiscrimination rule was intended for the private sector to keep tax-deferred savings plans from becoming tax havens only for upper-income workers. It acts to encourage companies to give incentives to lower-income workers to participate to the maximum.

Many people feel the antidiscrimination rule shouldn't apply to the federal government, since the thrift plan is open to all workers and since 95 percent of its 2.7 million full-timers make less than $50,000. Because many of the upper-income workers are political appointees, members of Congress and congressional staffers, there is keen, high-level interest in exempting the federal savings plan from the antidiscrimination rule.

Managers of the federal thrift investment plan have proposed legislation that would put the government program under the more liberal antidiscrimination rules that apply to many state and local government plans. Generally speaking, they require only that lower-income workers be eligible to participate, rather than basing upper-income worker contribution levels on the actual contribution level of lower-income workers.

Backers of the plan to put the federal thrift savings plan under the more lenient rules have met with staffers on the House Ways and Means Committee, which controls tax legislation, and the Internal Revenue Service. Key members of Congress are working quietly -- they think publicity could kill their effort -- to get the antidiscrimination rules changed. Meeting

The Charles County chapter of the National Association of Retired Federal Employees meets at 12:30 p.m. Thursday at St. Mary's Landing in Charlotte Hall. State Sen. Jim Simpson is the speaker. Call Kenneth Jones at 843-8188.