September and October are report card months for most of the 60,000 federal managers and supervisors in the Washington area.

Marks the so-called GM people get on a five-point rating scale used by most agencies will determine how much of a pay raise they will get -- more, less or the same amount -- compared with the 4 percent guaranteed next month for their million-plus white-collar subordinates.

The GM people -- there are 150,000 of them governmentwide -- are under a merit pay system created by President Carter's Civil Service Reform Act. Last year was the first time merit pay was implemented.

Fans of merit pay in government are as rare as Reagan buttons at a Kremlin reception. Put another way, most people under merit pay think the system stinks.

Grade 13, 14 and 15 personnel who were pushed into the merit pay pool had to give up the right to regular length-of-service pay raises (worth 3 percent) that come due, depending on time in grade, every one, two or three years. Those in-grade raises, which are in addition to regular October pay adjustments, are virtually automatic for most other federal employes.

Because of a tiff last year between the Office of Personnel Management and the General Accounting Office, most supervisors and managers got smaller raises than colleagues outside merit pay.

OPM wanted to put more money into the merit pay pool (which determines percentage increases for supervisors and managers) than GAO allowed.

This year's pay pool is made up of funds calculated this way: The amount that would go to provide a 4 percent pay raise; plus 1.6 percent to make up for in-grade raises denied GM personnel; plus an agency-determined amount between 0.1 and 0.4 percent of payroll, which is to compensate for quality-step increases the GM people can no longer earn.

Last year the in-grade equivalent amount was limited to 0.8 percent. That's the primary reason that few GM people got the big raises -- supposedly as high as 22 percent -- top performers had been promised in the reform act.

This year officials say things will be different. That is, better.

But nobody as yet appears to know exactly how the raises will be distributed, and how much (or how little) managers and supervisors will get.

In fact it is hard to find out what people got last year.

The Professional Managers Association, an outside group that thinks merit pay needs an awful lot of work, says nearly everybody got shafted in 1982.

PMA says that the vast majority of managers and supervisors -- regardless of good or bad marks -- got the same pay raise as subordinates. That works out to a loss, PMA says, since the merit pay people did not get in-grade raises they had formerly been entitled to receive.

OPM brass admit that things could have worked out better (they still blame GAO for penny-pinching at the last minute). But the payout was not as unfair, OPM says, as PMA and the Federal Managers Association claim.

Again this year merit pay people will be competing with their agency colleagues for the best grades (called performance ratings) and, they hope, the biggest raises possible. But until the grades are all in, and their agencies decide how to carve up the merit pay pool, nobody knows what those raises will be.