Thousands of federal employes, from small groups in the State Department to entire agencies like the Federal Supply Service, soon will shift over to the 4-day week.

Locally, portions of more than a dozen major government departments plan to experiment with the 4-day week in some form. Some will have employes work 10-hour days Monday through Thursday, or Tuesday through Friday. Others will experiment with "compressed" schedules that will give employes Friday, Saturday and Sunday off every other week.

Nationwide, more than 200 government organizations -- ranging from tiny offices to large agencies -- intend to adopt flexible work hours plans, compressed workweeks or a combination of both, within the next few months.

Several thousand civil servants here are already working under "flexitime." It permits them with their supervisors permission to come in and leave outside of "normal" work hours and rush hour. Agencies that have adopted it include the Geological Survey in Reston, the International Communication Agency and Office of Personnel Management.

Some engravers at the Bureau of Engraving and Printing have gone to a 4-day week, and some super-secret communications units of intelligence agencies have quietly shifted to the 4-day week.

Other action in the works:

Federal Supply Service, one of the major components of the General Services Administration, plans to convert most of its Crystal City operations to the 4-day week in early September for a test period.

Also next month, the Farmers Home Administration will put most of its 9,600 employes here and in the field on a variation of the 4-day week. FmHA will use what is called the 5-4-9 plan.

Typically under the 5-4-9 plan, employes over a two-week pay period would work eight, 9-hour days and put in one day of eight hours. The 10th day they would get off. By spliting offices under the plan, FmHA can have operations staffed the normal 5-day week with longer service hours for the public.

In Arlington, the Mine Safety Health Administration is also moving to the modified 4-day week with the 5-4-9 plan.

At least one unit in the State Department intends to convert to the 4-day week on an experimental basis shortly. Other State agencies may do the same thing.

Internal Revenue Service headquarters, considered a conservative management operation, is planning to shift some staffers to flexible working hours.

Environmental Protection Agency will go to the 4-day week at its Ann Arbor, Mich., motor vehicle lab.

A Social Security unit in Baltimore has already adopted the 4-day week.

General Services Administration's Boston region will experiment with the 5-4-9 plan. GSA had resisted the 4-day week until its new administrator, retired Admiral Gordon Freeman nudged top officials to test it.

A major government study of Washington area commuting patterns is due out in a few days. It is expected to prompt more agencies to experiment with flexitime, or the 4-day week. The idea is to ease morning and afternoon rush hours. In this respect, however, government is already doing a better job of staggering hours than private industry.

Under a relatively new law, federal agencies can waive overtime pay after 8 hours to test 4-day weeks if a majority of employes agree. In agencies where unions have exclusive bargaining rights, those plans must be approved by the union as part of a contract change.

If things go as hoped, some officials think a good number of the metro area's 350,000 plus civil servants will be on flexitime, or the 4-day week by mid-1980.