Within the next few months, the government's 20,000 top managers may be shifted to a new system with individual rank, custom-tailored pay scales, increased mobility and much less job tenure than they now enjoy.

Most of those officials - equivalent to corporation presidents and vice presidents in industry - live and work in the Washington area.

A half dozen options for a streamlined executive corps have been drafted by the Civil Service Commission and the Office of Management and Budget Federal agencies have been asked to comment on the proposals by Aug. 15. Then CSC-OMB brass will recommend one or more options to the President. He is expected to clear a new executive service corps proposal that could go to Congress by mid-September.

Top federal officials say revamping of the government's career and political executive system has top priority with the President, and they expect relatively quick - and affirmative - action by the Democratically dominated Congress.

The six options outlined by CSC-OMB yesterday vary considerably in style and scope. But all would accomplish certain things that are certain to be contained in the final legislative package Carter sends Congress. They include:

All the government's Grade 16 through 18 career and non-career officials would go into the new system, which probably will end up being called the Executive Managment System. Many Grade 15 workers in professional and managerial jobs also would be put into the EMS.

Veterans preference rights in selection, promotion or retention for jobs in the new management system would not count.

Employees entering the new management service would get away from the job-grade related system, and be assigned pay and levels corresponding more to military or foreign service rank. They would carry that rank or level with them regardless of what job they held.

Tenure as it now exists would be abolished for the executives. Two of the options would put executives on 3-year mutually renewable contracts to agencies. Others would provide only fall-back rights to other jobs if the candidate failed to measure up - as determined by his or her boss, a peer review board or some other oversight individual or group.

The number of career civil service executives probably would be increased and moved into jobs now reserved for political appointees. At the same time, political or noncareer individuals - now generally limited to the upper reaches of the bureaucracy - would be moved down into lower grades, closer to line management and in more field jobs.

The number of pay levels and salaries for each level would be set by the President and annual pay increases would be subject to congressional review. Bonuses, or some sort of financial incentives, might be set up in the new executives personnel system.

The options for executive managers are the first "white papers" to emerge from the Personnel Management Project which is housed at CSC, and headed by Dwight Ink, a respected, veteran bureaucrat on leave from American University.

CSC Chairman Alan Campbell said he hoped to get the final proposal - or proposals - to the President within four or five week, and to have a bill legalizing the changes before the Senate and House by September.