New regulations that would place new emphasis on performance and limit the effect of seniority in determining which federal workers are laid off and which qualify for within-grade (longevity) raises are scheduled to go into effect next month.

The changes would affect the 3 percent step increases that most workers now get automatically every one, two or three years in addition to general pay increases.

The regulations also would strip away some of the job protections longtime workers now have when their agencies are undergoing reductions in force (RIFs). During the first three years of the Reagan administration, about 2,900 Washington-area feds were RIFed under the last-hired, first-fired seniority system.

The Office of Personnel Management has been pushing for the performance-based pay and RIF system for several years. Congress blocked it in mid-1984, but that ban expires next month. The House, as part of a just-passed supplemental appropriations bill, would extend that ban for another year. Odds are the Senate will not act on the extension before the ban expires.

Former OPM director Donald Devine -- who argued that the system would be a boon to good performers and give more layoff protection to women and minorities (who often lack seniority) -- said the new system would be implemented in July unless Congress blocked it again. But he is gone, and congressional opponents of the new system are now negotiating with Acting OPM Director Loretta Cornelius for a delay or modification of the rules.

The rules would require employes to meet certain performance standards to qualify for the longevity pay raises and managers to pay more attention to grading employe performance. Currently, 99 percent of all workers who become eligible for the raises get them based on a "satisfactory" job performance rating, according to OPM. Under the new system, OPM estimated, about 96 percent of all persons eligible would still get the raises. During RIFs, employes would be given additional seniority credit based on their last three performance ratings.

Federal unions oppose the changes -- although most of them also disliked the policy of RIFs based on seniority -- because they say the system would make it too easy for managers to play favorites and punish otherwise innocent workers by giving them poor ratings that would deny them raises, or set them up to be fired when layoffs take place.