Nearly half of the government's top paid career federal executives who are eligible for the new highrisk, high-reward Senior Executive Service indicate they will join up this summer.

In most federal agencies, workers in Grades 16 through 18 (pay range $44,750 to $47,500) must decide by July whether to enroll in the SES. Those who do will have a shot at better pay, bonuses, special leave and retirement breaks. In return they will be under much greater pressure to perform, and required to take more frequent transfers or new job assignments.

Executives who stay outside the SES will retain their grades, pay and job security. But they will have little chance for future advancement.

Preliminary data obtained by the column shows that of 5,500 Grade 16 through 18 executives asked by their agencies about SES plans, 2,000 have said they will join up. Only six, so far, have said they will not go into the SES, which is the management backbone of President Carter's civil service reform.

Government-wide, the SES will take in about 8,500 jobs in the GS 16 through 18 range. About 10 percent of those slots will, as at present, be earmarked for "noncareer" or political appointees. Some jobs will be reserved for career executives. Most can be filled by either a career of noncareer type, so long as the overall 90 percent career, 10 percent noncareer ratio is maintained.

About 1,500 supergrade jobs already have been designated for automatic enrollment in the SES. Those jobs are either vacant or filled by incumbents who understand they must join the SES.

The big question is how many of the remaining career people - most of them here in Washington - will elect to go into the SES, or stay out of it. People hired for or promoted to most "supergrade" jobs after mid-July will have to join the SES.

The Office of Personnel Management has surveyed most of the major federal agencies and departments. So far, indicators show an overwhelming number of executives will join up. But the 2,000 "yes" and only six "no" responses do not tell the whole story since they represent only about half the total.

It is to be expected that those ready to make the big career change by going into the SES, would say so early. Those who are having doubts, or who wouldn't touch the SES with a 10-foot pole, obviously will wait until the last minute to commit themselves.

A few agencies, who advised executives early of the SES and its options, have set a mid-June deadlind for the final decision. Most executives will have until July 13 to say yes or not to the SES.