In addition to the 4.1 percent raise that white-collar federal workers will get in January, the new salary law allows the president to give a pay differential of up to 8 percent to employees in high-cost areas where the federal government has recruiting problems. Sounds tailor-made for Washington, right? Not necessarily.

The bad news for locals is that metropolitan Washington may not be one of the places on the special geographic pay raise list for next year or 1992. At least two reasons for this:

First, there are many cities -- New York, Los Angeles, San Francisco, Boston, Hartford, Honolulu, San Diego and New Haven among them -- where overall living costs are higher and where the government is having a very hard time getting and keeping people. Depending on data developed by the Bureau of Labor Statistics and on the government's recruiting and retention experience, metropolitan Washington might not qualify for special pay treatment. An estimated 58,000 of the area's 360,000 federal employees are already paid special higher rates because they are in hard-to-fill jobs.

Second, giving federal white-collar workers in metropolitan Washington a special 8 percent pay raise would cost $738 million a year. For that kind of money, the administration could give the same raise to each federal worker in the nation's 10 biggest cities. That gesture could buy a lot of political goodwill beyond the Capital Beltway.

In his original budget, the president proposed the 8 percent differential for San Francisco, Los Angeles and New York. No cities or areas were cited in the pay package that became law. But it will be up to the president and his advisers to pick which cities get them. And the Washington area may not be on the A list. Investment Options

Some workers say they are getting bad advice from their agencies about thrift savings plan investment options. Starting next year, you can invest your contributions, past or current, in any or all of the savings plan's Treasury, stock or bond options.

The savings plan is an optional part of the federal retirement program. It allows workers to save or invest via payroll deduction. Money invested and its earnings are tax-deferred like a private-sector 401(k) plan.

People covered by the old (Civil Service Retirement System) pension plan can invest 5 percent of pay. Those under the new Federal Employees Retirement System can invest up to 10 percent with a 5 percent government match. The open season for enrolling or making investment changes starts a week from today.

Some workers say their personnel or benefits offices aren't aware of the liberalized investment rules. Lump-Sum Seminar

Government Retirement Benefits Inc. will have a half-day seminar Nov. 17 on the lump-sum pension benefit option. Workers who retire by Nov. 30 will be able to take the lump-sum payment. Beginning Dec. 1, the option will be eliminated (for at least five years), except in rare cases. The seminar will be at the Ramada Renaissance Hotel. For information, call 703-461-9100.