The 120-day legal honeymoon between the Reagan administration and the Carter-created Senior Executive Service ends May 19. After that date, political appointees of the new regime may begin to issue new performance ratings for more than 6,000 career SES members who, if they get bad marks from the boss, can be booted out of the $50,000-per-year-plus elite corps of government executives.

SES is a creature of Civil Service Reform. It took in most of the career jobs at the supergrade levels (Grades 16, 17 and 18). Recruits who joined the SES (and 95 percent did) traded in tenure -- and job security when administrations change -- for the chance at bonuses, higher pay and faster promotions within the SES.

At the end of February, the SES had 7,346 jobs filled and 1,824 vacancies. As of last fall, 500 of the political (noncareer) slots within the SES, which is a mix of career and political executives, were filled. Most of the noncareer SES people probably will be replaced with Reagan appointees. Many of the jobs already have been filled with Republican appointees. Overall, SES has an authorized job strength of 9,200 slots, about 950 of them political, the rest career.

By law an incoming administration is prohibited from involuntary transfers of career SES members until 120 days after the agency head takes over. That countdown will vary from agency to agency, depending on when the boss takes office. But the first 120-day hands-off period ends in mid-May.

After May 19, federal agencies may begin issuing new performance evaluation ratings for SES members. The ratings determine whether they stay, or go. Idea of the 120-day countdowns was to establish a getting-to-know-you period during which new political appointees would work with and evaluate career bureaucrats they inherited with their departments and agencies.

There is no indication -- yet -- that the Reagan people intend to clean house. But the CS Reform Act makes is possible. Congressional Democrats will be watching to see what changes are made within the career SES. If the Reagan people clean house, either by transferring-people-until-they-quit or giving them bad ratings, there will be bowls raised in Congress. And it could set a precedent for bureaucratic bloodshed each time the White House changes hands. p

Some Reagan appointees are pleased with the career executives in their agencies. Others are convinced that the career SES was loaded up with officials whose main claim to fame is that they were loyal Democrats. The White House and Office of Peronnel Management are aware of a number of last-minute job changes that gave noncareer appointees career SES jobs. Those are the first places where the fur will fly.