More than 260,000 federal workers who now get automatic pay raises would be put into a revised merit pay system alongside their bosses under legislation the Senate Civil Service subcommittee takes up today.

The new folks in the merit pay pool would include everybody in grades 11 and 12. Those employes, like most other U.S. workers, now get automatic annual pay raises (when there are any) and additional length-of-service raises worth 3 percent every one to three years.

The idea of expanding the merit pay system has an excellent chance of clearing the subcommittee because its chief backer, Sen. Ted Stevens (R-Alaska), is the chairman.

Stevens' inclusion of GS 11 and 12 workers into the merit pay system (which already covers 175,000 higher grade supervisors and managers) is designed to stop the Reagan administration from making even deeper changes in the federal personnel system simply by changing the rules.

The vehicle Stevens is using is a bill before his subcommittee that is designed to put more carrot and less stick in the current merit pay system for supervisors and managers.

Under the merit pay system set up by President Carter, supervisors and managers must compete for pay raises and are not eligible for within-grade increases. Despite its competitive nature, the current merit pay plan often permits poor performers to get the same increases as those with satisfactory ratings.

Fans of merit-pay-as-it-is could probably all fit into a 1960 VW Beetle. That is why Virginia Republican senators Paul Trible and John Warner and Rep. Frank Wolf are pushing a bill to reform it, and why Stevens is using their bill to get his changes made.

Trible, Wolf and Warner come from a state with 150,000 federal workers (only California, New York, Texas and the District have more) who are anxious to have the merit pay system reformed. Those workers are fearful of pending administration rules changes that would devalue seniority and base most major personnel actions on employes' last performance ratings.

Stevens wants to include in the merit pay bill a formula that would force agencies to consider both seniority and performance when determining who is to be RIFfed. The current rule is that the last hired is the first fired.

President Reagan wants to base firings on performance, rather than seniority. Stevens would assign points to years of service and an employe's last three performance ratings, and workers with the fewest points would be laid off.

If federal unions want more time to study the Stevens plan, the chairman may push the Trible-Warner-Wolf bill through subcommittee without his amendment to extend its coverage. If that happens he will put the new language on the merit pay bill when it reaches the Governmental Affairs Committee.

The Office of Personnel Management says it will put its reforms into effect administratively unless Congress is well along with its own plan by Aug. 1. The OPM estimates it would take about 60 days to put the new RIF rules into effect and between 120 and 180 days to put the new performance incentive program into operation.