Army, Navy, Air Force and the Marine Corps would be required to make a gradual 6 per cent reduction in top civilian jobs under legislation approved by Senate-House conferees.

Although the cut would be tough, Defense officials realize it could have been worse if a Senate plan, which would have doubled the number of jobs to be cut, had prevailed.

As approved by a Senate-House conferees, the Defense authorization bill will require Defense the largest employer in the Washington area to make a 6 per cent annual reduction in Grades 13 through 18 jobs over the next 16 to 24 months. Defense has about 60,000 people in those grades, many of them here. Salaries at that level range from $24,308 to $47,500.

Those jobs cuts are linked to a similar reduction in the number of admirals and generals. It would mean slower promotion tasks in both the civilian and military side of the Defense Department.

The good news, for federal workers, is that the Senate conferees dropped a Senate-approved rider that would have extended the grade reduction down to Grade 12 of the civil service. There are about 62,000 employees at that level. It pays from $20,442 to $26,571.

The 6 per cent reduction, which Congress is certain to clear and send to the President, is in addition to cuts already made in high-grade jobs. Defense - particularly Army and Navy - has gradually been reducing the number of middle and high-grade jobs. But the Pentagon will not get credit for any of the cuts already made.

Credit for turning the Senate conferees around goes, in part, to Sen. Alan Cranston (D-Calif.). He wrote a serious Dear Colleague" letter to conferees arguing against overly tough cuts. Cranston's state has the largest concentration of federal workers, and many of them are with Defense units.