The long wait isn't over for thousands of special-rate federal workers. For the past several years, nearly 30,000 of them have been looking for a special fat government check for raises denied them between 1982 and 1988.

Each week, dozens of the special-raters, some retired, some in private industry, call or write. Subject: Is the check in the mail?

Most are engineers, scientists or medical personnel. They were in special pay status during the period when the government stopped automatically giving them the same January raises that went to other federal employees. Although most special-raters still enjoy a 2 percent to 30 percent pay differential, the National Treasury Employees Union sued, seeking to recover the full amount of the general pay raises.

After a complicated and lengthy battle, an appeals court directed the U.S. District Court here to act as referee between the Office of Personnel Management and the union. At a Jan. 30 "status conference," it will ask OPM and NTEU if they have reached agreement on a back pay settlement. Both parties will say no.

NTEU wants full back pay, which would cost millions of dollars. OPM wants a pro-rated payback. That would give most employees less than the full amount, and some no back pay at all.

Although the court could rule immediately, it is likely to set a date for oral arguments on the back pay case.

Point of all this: If you are one of the special-raters, don't budget your summer vacation (or Christmas) in anticipation of back pay. Break in Service

Thousands of people who returned to the federal government after a break in service will be able to buy back lost service time to boost their pensions by making monthly installment payments taken from their annuity checks.

The new feature is automatic for anyone retiring after Dec. 1, 1990. Many, if not most, people who leave government service withdraw their contributions to the retirement system. For people under the old Civil Service Retirement System, that is about 7 percent of their total salary. Those who return to the government and retire lose their past service time unless they repay the money with interest. Although everybody should buy back their lost time to boost their pensions, many can't afford to do it in one lump.

The new law allows anyone retiring (except on disability) to make the redeposit in a single check or by monthly installments after retirement. Lost Lover Department

Information sleuth Matthew Lesko makes a living telling people how to get information from Uncle Sam. His Valentine's Day angle: Federal assistance in tracking down an old flame. His book suggests getting his/her last known address from the U.S. Postal Service (it costs $1); asking Social Security to forward a letter; or calling the federal Inmate Locator Hotline, 202-307-3126, if you think your significant other is doing time. For gold diggers, Lesko says 47 states will, for a fee, give you a list by Zip code of singles who drive BMWs or Mercedes. Looking for Lesko himself? Call 301-942-6303.