If you can't judge a book by its cover, you soon may be able to guess a federal employe's GS rating by the style of his or her desk.

An 18-month freeze of government purchases of new furniture has been lifted and the General Services Administration has weighed in with a temporary regulation defining who is eligible for specific types of office furniture.

Only members of the Senior Executive Service, their bosses, and military peers qualify for "executive" furniture, those large, all-wood desks that cost $600 on average, according to a spokesman for the Federal Supply Service. Subordinates in the GS13 to GS15 levels must settle for part-wood, part-veneer "middle management" desks that average $260 each.

Those in grades GS1 through GS12 get "general office furniture," the basic battleship gray steel desk that costs about $240.

GSA has been scrutinizing government furniture purchases since it imposed the buying freeze in October, 1979, after newspaper reports and testimony before Congress told of agencies purchasing new furniture when they had plenty on hand.

A General Accounting Office auditor testified that he saw 2,000 pieces of furniture stashed in an Agriculture Department basement and $38,000 in new, largely unopened cartons of furniture in one of the department's attics, even though the department continued to buy new furniture.

Subsequent GSA investigations revealed that more than $8 million in government-owned desks, tables, chairs and other items -- some of them new-- were found gathering dust. In all, about 75,400 pieces of furniture were sitting in government basements, attics and warehouses across the country. According to the supply service, all of that furniture has either been placed in service by the agencies that stored it or transferred to other agencies that could use it.

In the Washington area, the supply service's "Operation Clean Sweep" located 39,641 pieces of stored furniture. About 35,800 items were returned to the agencies that had stored them.

The Office of Management and Budget extended the GSA freeze in February, 1980, and added other items, such as appliances and photographic equipment, to the list of unbuyables. The freeze was lifted agency by agency about a year later as budgets, including reduced appropriations for such items, were approved.

OMB excluded from the freeze items such as military equipment other than furniture, equipment needed to protect health and safety, and equipment produced by Federal Prison Industries, the National Industries for the Blind and National Industries for the Severely Handicapped.

Furniture purchases through GSA dropped more than 50 percent, from $271.9 million to $132.9 million from fiscal years 1979 to 1980, the supply service reported.

Now that furniture buying can proceed, GSA's new regulation attempts "to create uniform standards" for future purchases, said John M. Allen, assistant commissioner for property management.

Agencies are responsible for making sure that their employes have appropriate furniture, he said. Some agencies already had such standards, but in other cases middle-management personnel managed to obtain executive furniture for their offices.

Some federal employes will still be able to present a more glorified front to the public than their rating suggests. That's because the new regulation also provides that secretaries and staff assistants "whose duties are in direct support" of executive and middle-management personnel working in adjacent areas may be allowed furniture similar to or matching that of their superiors.

The temporary regulation will be in effect through next July, by which time GSA will decide what form a more permanent rule should take. CAPTION: HOW TO TELL A BUREAUCRAT BY HIS DESK; Picture 1, The executive desk, for seniior executive service, their military counterparts, and above $600 average.; Picture 2, The middle management desk, for GS 13-GS 15, $260 average.; Picture 3, The general office desk for GS 1-GS 12, $240 average. By James A. Parcell -- The Washington Post