It could be many months before 120,000 engineers, scientists, nurses and typists who are paid special rates higher than other federal employees learn if they will get multimillion-dollar catch-up raises dating to 1982.

The back-pay case is before the U.S. Court of Appeals for the Federal Circuit. Government briefs opposing the raise are due this month, and the employees' written argument for the raises isn't scheduled until April. That means oral arguments, and a decision, are a long way off.

If the ruling favors workers, it would mean retroactive raises of up to 10 percent, plus six years' back pay for some employees. The raises would also increase the size of their future pension checks.

A victory for the special-rate workers would cost the government (taxpayers) a bundle, and create a nightmarish job for agencies that would have to reconstruct job and pay histories for thousands of workers. Some will have left government, retired or died.

Locally 40,000 people, ranging from engineers and scientists in exotic specialties to clerk-typists, have a stake in the back-pay struggle.

All of the special-rate workers are paid higher salaries than other civil servants in the same grades because the government has trouble hiring or keeping employees in their fields. Salaries for the special-rate employees can be as much as 30 percent higher than those of other civil servants in the same grades.

But for some special-rate employees, the pay differential has slipped since 1982 when the government, for reasons of economy and management, stopped automatically giving them the general federal pay raise.

Last spring, for example, the government added more than 30,000 clerical workers in the Washington area to the special-rate category. That was good news when the employees received increases of 3 percent to 23 percent. But it soured in January when the clerical workers -- many of whom were unaware of the mixed blessings of special status -- learned that they wouldn't be getting the 2 percent general pay raise.

The National Treasury Employees Union has won the first round in the fight to get both kinds of raises -- special and general -- for the special- rate people. Last March the U.S. District Court here said the special-rate workers are entitled to back pay and raises equal to those granted other employees since 1982. Regular federal workers got 4 percent raises in 1982 and 1984; a 3 1/2 percent increase in 1985; 3 percent in 1987; and 2 percent this year.

The government is fighting the back-pay order partly because of its cost in dollars and paper work, but also because officials believe it would cut into the government's authority to set special pay rates -- by job, grade or geographic location -- to meet specific recruiting problems. That's why the government is likely to appeal any order, and why it will be a long time before the issue is settled.Job Mart

Federal Energy Regulatory Commission needs legal clerks (typing), Grades 4 through 6. Call 357-5410.

Navy needs a computer scientist and electronics engineers, GM (merit pay) 14. Call 697-6181.