A reorganization-related power struggle under way within the addministration could mean basic changes in job security for thousands of federal workers now covered by the proctective blanket of civil service.

The first test will come when President Carter tells which agencies he wants in his planned new Department of Energy. More than half the workers now slated as the cadre for that departments are already under the so-called expected service, rather than civil service.That means competition for jobs and to some extent tenture security are different from the regular civil service.

Like their predecessors from the Eisenhower to Nixon administrations, some new Carter appointees are already frustrated by the lack of control and responsiveness - as they see it - of an entrenched bureaucracy and its rigid hiring, firing and job status rules.

One way to avoid some of the "problems" of civil service procedures in the new Energy Department would be to put all employees into the "excepted service" rather than the career civil service.

A number of agencies - CIA, FBI, National Security Agency, Federal Reserve Board among them - already have their own excepted serivce personnel systems. They are based on the civil service and follow most CS job guide lines, But agencies heads are much freer to deal with personnel than those whose bureaucracies are under strict civil service.

Two certain candidates for the new Energy Department are the Energy Research Department Administration and protions of the Nuclear Regulatory Commission. They were born out of the split up of the Atomic Energy Commission and retain excepted service status (like the AEC had) for their employees. ERDA has 8,300 workers and NRC about 2,500.

One major advantage of the excepted service, some administration aides have learned, is that hiring is handled directly by the agency rather than through the slower process of drawing candidates from a government-wide pool of applicants, as under the civil service.

Two agencies that might come under the new Energy Department are the Federal Power Commission and Federal Energy Administration. FPC has 1,379 workers, most of them here. FEA has 1,926 headquarters aides and another 1,687 in the field. Both agencies are under the civil service system, except for lawyers and political appointees who are in the expected service.

Proponents of a get-it-done Energy Department argue it could move quicker and more decisively if new employees - from FPC, FEA and elsewhere - were put under the excepted service rather than civil service. They wouldn't lose government longevity time, pay or benefits, but they would be subject to tighter management under the excepted system.

Insider say that White House energy czar James Schlesinger Jr., is leaning toward the idea of making the Energy Department the first cabinet-level operation under the expected service.

The Civil Service Commission - which still doesn't have a chairman to speak for it - is quietly fighting the idea of taking civil service job status away from anybody.

The argument is that it would damage morale, set a bad precedent in other reorganizations and be unfair to employees who signed up under civil service. CSC's argument is that the energy department - like State and other agencies - could operate effectively with two separate personnel systems.