The Reagan administration this summer will take another shot at changing federal work rules to give greater weight to performance and less to seniority when decisions are made about pay raises, promotions, firings and layoffs.

Congress last year blocked the Office of Personnel Management from implementing the rules change, which OPM contends would most benefit women and minorities. That congressional ban expires July 1.

OPM plans to put the new rules in effect by mid-summer if Congress doesn't block the plan again.

The proposed performance- based incentive system links within-grade (longevity) raises to workers' annual performance ratings.

Those longevity increases are worth 3 percent. To get one, an employe would have to have a current performance rating of "fully successful" or better. Workers come due for the raises every one, two or three years, depending on their time in grade.

Under the plan, managers would be encouraged to spend more time rating employes, because OPM officials believe the present within-grade raise system has become automatic.

OPM says 99 percent of all workers now get raises when they come due. Under its new tougher grading system, OPM estimates that about 96 percent of employes would get the within-grade increases. That would mean that about 20,000 workers who now get raises each year would be denied them.

Layoffs, which the government calls reductions in force, would be based on a combination of seniority and performance ratings. Currently, seniority is the dominant factor in job security.

Under the new performance plan workers in agencies undergoing RIFs would be ranked on a point system. Employes would get one point for each year of service, plus points based on their three most recent performance ratings.

Workers would get 10 points for each "outstanding" rating; seven points for a rating of "exceeds fully successful" and five points for a "fully successful" rating. Workers would not get any points for a rating of "minimally successful" or "unacceptable."

The system would make it possible for a long-time employe with average-to-poor ratings to be fired before a newer worker with top marks.

OPM contends that the system will be especially beneficial to women, who on average have less seniority than men. But federal unions and managers' groups, all of whom oppose the new system, contend that it would make it easier for bosses to punish employes for political or personal reasons by giving them low ratings that could deny them within-grade pay raises, or put them on hit lists when agencies are undergoing layoffs.