The White House has agreed to a gradual phase-in of its plan to put 70,000 federal managers in Grades 13 through 15 under a strict, merit-only pay system.

Part of the president's civil service reform package would remove the managers from the automatic annual pay raises that other government workers get each October.

Under the original "reform" bill sent to Congress, federal agencies could have removed GS 13, 14 and 15 managers from the automatic pay raise category as soon as the bill was signed into law. But earlier this week, the White House advised the Senate that it would phase in the merit pay system gradually if the reform bill becomes law.

Eventually, however, everbody in those grades in a management position (the grade pay range is from $26,022 to $47,025) would be taken off the automatic annual pay cycle. Instead, those managers would be given all, part or none of the regular annual raises that their subordinates get automatically each October. The amount they get would depend on what their bosses think they are worth.

The merit pay plan sounds good in theory. In practice, however, some managers believe that separating them from the automatic raises would subject them to even greater pressure from bosses to do things that they might consider improper.

At any rate, the Carter administration has agreed to phase in gradually the merit pay for supervisors, with tests being made by agency, and perhaps even by grade, with follow-up reports to show how the system is working.

Senior Executive Service: The administration's proposal for an elite corps, taking in all 9,200 federal "supergraders", is part of the reform bill the Senate and House will begin writing next week.

Presidential aides say the new higher risk job system for Grade 16, 17 and 18 workers would give better pay and retirement incentives to top executives, and would make it easier to transfer or remove people who don't measure up.

Enthusiastic White House planners estimate that at least 8 of every 10 incumbent supergraders would join the SES voluntarily. Once the bill becomes law, anybody taking a supergrade job would have to become an SES member.

Officials believe that executives like the SES because few have complained about it to people selling the plan. But they have been complaining to other people. The fact is that many supergraders are worried about the SES and its effect on their jobs, and the top management of government.

With that background, here is a portion of a position paper that one 20-year man, a supergrade veteran of three agencies, has sent key members of Congress. It shows some of the doubts certain supergraders have about the motivation behind the SES. It reads in part:

" . . . Under the current system, job security is very firm. Before this system is scuttled, much thought should be given to the effect on the functioning of civil service. To suppose the end result will simply be an increase in efficiency, because competence will be rewarded and incompetence punished, is simplistic.

"Under the SES the entire system would become more authoritarian. The relative strength of the executive branch as opposed to Congress would increase because the bureaucracy would become more simply an instrument for carrying out policy decided at the highest levels, and the contrary opinions and experience of the working level people would tend to be brushed aside."

The nervous supergrader notes that the SES is "designed to make job performance the central criterion by which managers are retained and compensated."

"This emphasis on reward of competence and punishment of incompetence is misplaced and misses the point. Under SES, the job security of the individuals concerned will become central to their way of dealing iwth the government's problems.

"In taking a position, for example, in opposition to someone of importance in his department, or of higher rank, a civil servant under SES will be conscious of taking a significant risk. And effective reprisals will be at hand for those who have the temerity to express views which may irritate some senior government official.

"The ability of the civil service to deal with conflict situations, and such situations are endemic in government, will be materially weakened by the introduction of the factor of the job security of the individuals who are involved with making choices which should be made on their merits."