Approximately 150,000 key workers in Grades 13, 14 and 15 -- about three of every four people in those civil service grade groups -- will be shifted to a complex, controversial merit pay system beginning this year.

By October 1981 everybody in those grades who is designated as either "manager" or "supervisor" will be in the performance pay area. It takes them off the automatic pay raise cycle, and will force them to compete against each other for October raises.

In rank-conscious Washington where officials outnumber clerks there are more than 65,000 in just those three grades. Pay for them ranges from $29,375 to $50,112.50. An even larger percentage of the Washington crowd is expected to be put in the merit pay pool.

Merit pay probably has caused more concern in the bureaucracy than any other feature of President Carter's civil service reforms. When fully operational, supervisors and managers will be rated and rewarded by their bosses while people in other grades and nonsupervisory types get full, regular raises. The supervisors and managers will be guaranteed only half the regular October raise. To get more they will have to earn it, in the eyes of their bosses, who also will be under merit pay. Money to finance the merit raises will come from regular salary dollars for the GS 13 through 15 group plus funds from longevity raises and other boosts that no longer will be given.

Many potential managers-supervisors have misgivings over the merits of merit pay. They fear bosses will be tempted to shave them, financially, so there will be bigger bucks for the top grades -- the big bosses.

Officials backing merit pay point to the way it operates in private industry. Some GS 13, 14 and 15 people, familiar with the way merit pay sometimes works in industry, are not ressured by the comparison.

Several agencies plan to have the required performance appraisal systems in the place this year. They can begin merit pay for their GS 13, 14, and 15 personnel this October.

Federal unions report an upsurge in inquiries from GS 13, 14 and 15 personnel who -- in the past -- have tended to let lower level workers do the unionizing.

A new group -- called FED 42 -- is being formed out of the GS 13, 14 and 15 personnel who will go under merit pay. (Add 13, 14 and 15 together and you see where FED 42 comes from). Leonard Burchman of Labor is president.

Other officers of FED 42 include Ann Macaluso, Transportation; Dr. Richard Lancaster, VA; Frederick Drayton Sr., Labor; Richard Taube, Federal Communications; Joseph R. Julianelle, Labor and Robert M. Johnston also from Labor. The group pledges to work for improved professionalism among the mid-management group, but one suspects it was born to serve as a watchdog on the merit pay system about to be put into play.