Washington is on the verge of a leisure time revolution that could reduce eye-burning air pollution, cut commuting times and improve the cash-flow of restaurant and resort owners.

Or it could make it all worse. Time will tell.

What is happening is that at least 5,000 federal workers here are now on the four-day work week. Another 10,000 at least, are working on "flextime" schedules that permit them to set their own hours, arriving late or leaving early, or taking more time for lunch, shopping or whatever.

Nobody is quite sure what the effect of the changes will be, except that the way we drive, eat, relax work for or deal with Uncle Sam will change.

Federal officials here -- and in Denver -- are watching the growing trend of flextime and four-day week to see what it could mean for the government, private employers and just about everybody living in or near big cities.

Denver's federal community shifted to the four-day week sometime ago to fight air pollution. About 15,000 civil servants in the Mile High City, which has one of the nation's worst air pollution problems, are working a 10-hour day, in return for a long weekend. The theory is that it gets a large number of commuters off the freeways one day a week.

Washington will be a bigger test since nearly half a million people here -- most of the area's adult workers -- work for the government as civilians, or in uniform.

There are two kinds of four-day week experiments going on now. One is the straight four-day week, with 10-hour workdays and a three-day weekend every week. The other is the so-called 5-4-9 plan in which employes work four days of nine plus hours one week four days the next and get two long weekends a month.

Agencies experimenting with the four-day week, or the 5-4-9 plan here include portions of the Bureau of Engraving and Printing, Army's Management systems support at the Pentagon; the FBI's records management division; Agriculture's office of governmental and public affairs the Coast Guard administrative offices and the Federal Supply Service of the General Services Administration. Some shut down the whole works on Fridays or Monday. Others stagger days off and provide services 10-hours a day, five days per week.

Three federal hospitals -- the Public Health Service facilities in New York and Seattle and a Veterans Administration hospital in Los Angeles -- are on the four-day week. They still are open 24 hours a day, seven days a week. The flexibility of the system allows more key employes, doctors and nurses, to get the benefit of a long weekend from time to time.

Many agencies here, or portions of them, are using flexitime. Under the system, employes can come in and leave when they choose (with supervisory approval) so long as they put in an eight-hour day and are on hand during the so-called "core day," which might be from 9 a.m. to 3 p.m.

Agencies using flexitime are the Geological Survey in Reston; several components of the Commerce Department; parts of GSA and Labor, State Department's passport office and the Office of Personnel Management. Officials in charge of the program say the figure of 10,000 workers under flexitime is "conservative". They expect thousands more workers will go under it, or the four-day week this year.

Federal officials monitoring the flexitime experiment are trying to find out if it decreases -- or increases -- the miles workers drive. Five hundred employes here are participating n a test to determine if they spend less, or more, time in cars under the four-day week.

Results of the test will have a major impact on firms and service groups here who deal directly with the government in some form or other. Merchants from Arlington to Ocean City are also anxious to see if people spend more time in restaurants and stores, or become accustomed to minivacations because of changing work styles.