The Reagan administration won two rounds this week in its fight to base raises, promotions and layoff protection for federal white-collar workers on how well they do their jobs rather than how long they have held them.

On Wednesday, the House rejected a Treasury-Postal Service-General Government supplemental appropriation bill that had a rider that would bar the administration from making any work-rule changes until Sept. 30, the end of this fiscal year.

Although the bill was not killed because of the rider, offered by Rep. Steny Hoyer (D-Md.), administration officials have repeatedly warned that the president will veto any bill containing such language.

The timetable is important because the Office of Personnel Management says it will make the rules change on its own unless Congress is "seriously" working on its own performance pay plan by Aug. 1.

If OPM follows that schedule it would mean that the new performance system, which would link within-grade pay raises and certain promotions to an employes' most recent performance rating, could be in effect as early as February. And the new RIF regulations, in which performance rather than seniority would protect employes from layoffs, could be in operation some time in November. That month, in many agencies, is the start of the firing season.

Yesterday, plans to come up with a legislative compromise to the OPM rules were put on the back burner when federal unions objected to the changes at a hearing of the Senate Civil Service subcommittee. The only member of the subcommittee who showed up was Chairman Ted Stevens (R-Alaska).

The American Federation of Government Employees, which was supposed to testify first, boycotted the hearing. Copies of the Stevens amendments, which he wants to add to a pending merit pay bill, were delivered to federal unions late Wednesday afternoon. Some said that the changes were not what they had been promised.

AFGE President Ken Blaylock said it looked as if the amendments had "been written by the OPM," not by a committee truly trying to draft a compromise.

An AFGE spokesperson said the amendments proposed were "far different" from the plan Stevens had outlined earlier.

Stevens has said he wants to block the OPM rule changes by legislating--as a rider to a pending merit pay bill--his own changes. They would count both performance and seniority during RIFs, and put more workers under a modified merit pay system.

Although Stevens agreed to meet again with union leaders to iron out a compromise, he warned that time was running out and that if Congress doesn't act OPM will put its own plan into effect.

Union leaders left the hearing with the impression that another hearing would be called next week. But a subcommittee aide said there will not be a hearing next week.

Stevens made it clear that he does not consider OPM's Aug. 1-or-else deadline binding. But OPM does. And the clock is ticking.