The Fed of the future very likely will: Set his own hours, maybe working a four-day (or even three-day) week, use less sick leave, rarely be late for work, take super-long lunch hours and yet provide better service to the taxpayers than his 1978 counterpart.

The above is not an outline for a Federal Triangle 1999 science fiction series. It is a glimpse at the way thousands of Washington area civil servants may be doing their jobs within the next couple of years.

Flexitime, the set-your-own hours program, already is here for 32,600 of the area's civilian federal workers, and it will grow and spread beyond the 80 U.S. installations from Reston to California that now are allowing employes to vary their schedules within an expanded workday.

Under on-going experiments, more than 175,000 non-postal federal workers nationwide - nearly one in every 10 - now are under some kind of flexible hours program. It permits them to come in and leave when they want, provided they are in the office for specified periods each day and put in the standard 40-hour week. Some agencies already have a few employes working 10-hour days four days a week, giving them the long-dreamed of three-day weekend.

Last week the House passed legislation that would step up the pace of flexitime experiments in government and, by waving the mandatory overtime-after-8-hours law for consenting workers, permit agencies to experiment with four-day and even three-day workweeks on a very limited basis.

The Senate Governmental Affairs begins hearings soon on the flexible hours work experiment and backers are optimistic it will be passed and signed into law this year.

When that happens, the Civil Service Commission will step in with guidelines for agencies, telling them how to go about setting up flexible working hours schedules for their employes. The test period will run for three years. During that time some officials hope to double or triple the number of employes who abandon the 9 a.m. to 5:3o p.m. workday for flexitime.

In addition to requiring agencies to test flexitime, the pending legislation would allow no-cost tests of the four-day week by permitting federal agencies to waive overtime pay for workers who opt for a 10-hour days to get an extra day added to their weekend.

Among the Washington area's 100-plus federal agencies, with more than 350,000 workers, the Defense Department already has 6,800 people involved in flexitime experiments. Other agencies (and numbers of employes) already testing the program are Agriculture, 3,992; Commerce, 4,000; HEW, 6,470; Interior, 3000; Justice, 45; Labor, 100; State, 20; Treasury, 1,500; Civil Service Commission, 4,000; Law Enforcement Assistance Adminsitration, 600 and Environmental Protection Agency, 2,500.

Backers of the program stress that the taxpayers should, and will, be the biggest gainers even though they expect it will improve employe moral and give workers more freedom to tailor their work around personal and family needs while giving them more leisure time.

Some of the benefits from flexitime are expected to be:

Stretched-out service hours to the public with agencies like Social Security. IRS and others having service and information offices open from 10 to 12 hours a day, and perhaps all day Saturday.

Less traffic congestion with people staggering their own working hours and perhaps making greater use of public transportation.

Reduction of short-term absences and the virtual elimination of tardiness.

Improvements in employe morale and productivity, based on previous tests in government and industry.

Officials agree that the flexitime could have many drawbacks, and that it will take a more sophisticated supervisory force to make sure that the program is not abused. They also say that some increased energy costs could be expected if agencies are open longer. But these might be offeset by reducing traffic jams and increasing use of public transportation.

The only limits to the flexibility of the flexible hours working program are the constraints of the 40-hours week the government still maintains. Because federal work schedules are set in two-week blocs, it would be possible under flexitime to have an employe work 50 hours in one week and 30 hours (three 10-hour days) the next week.

If the Senate moves quickly on the legislation, thousands of additional federal employes could be working under the set-your-own hours program by early fall, and begin working out four-day weeks for themselves by this time next year.