The Senate Civil Service Subcommittee next week will report out a bill designed to head off the administration plan to base white-collar pay raises, promotions and job security on performance rather than seniority.

Subcommittee Chairman Ted Stevens (R-Alaska) wants to set up a point system that would consider employes' seniority and their last three performance ratings and would be used when agencies are undergoing reductions-in-force.

Stevens, the Senate's assistant majority leader, would also reform the merit pay system, which now covers about 150,000 Grade 13 through 15 supervisors and managers, and extend it to all employes in Grades 11 through 13.

The vehicle for the changes is the merit pay reform bill of Sens. Paul Trible and John Warner of Virginia. Stevens, who is up for reelection next year in a state loaded with U.S. workers, hopes it will run over the administration plan to base major personnel actions on performance rather than seniority.

Administration officials have said that they will put the rules changes into effect on their own unless Congress has acted on the matter by Aug. 1. An aide to Stevens said yesterday, however, that the Aug. 1 deadline is OPM's, and not Stevens'. He wants Congress to have until mid-September to act on the changes.

If administration officials stick to their Aug. 1 timetable, he said, Stevens will rally Senate Republicans to block them. On the House side, Democrats, led by Reps. Steny Hoyer (D-Md.) Mike Barnes (D-Md.) and Bill Ford (D-Mich.) have said they will not permit the administration to make changes without going through Congress.

Under the modified merit pay system, employes who got "fully successful" performance ratings would get regular within-grade raises as well as the full amount of the regular October federal pay raise. Those who got better ratings would also be eligible for one-shot annual cash bonuses.

When agencies were undergoing RIFs, a point system would be used to decide who gets fired. Employes would get one point for each year of service. Workers with "outstanding" ratings would get six points; those with "exceeds fully successful" five points; "fully successful" three points, and "minimally successful" one point. Their last three performance ratings would be considered and points for them added to service time.

Given the congressional opposition to the Reagan performance plan, it is hard to see how the administration is going to be able to meet its August reform deadline unless Congress loses interest in blocking them, which is what the White House is counting on.