HISTORIANS LOVE to figure out when one era ends and another begins. The dates are usually impossible to fix with any certainty because the people at the time are either unaware that a new era is beginning or they neglect to record what is happening. I would like to fix that. A new era has begun in Washington. A city employe has been fired.

Actually, two city employes were fired. They were dismissed for doing nothing more than doing nothing. That this is a firing offense must have come as something of a shock to them since there is, in this and most cities, something of a traditon that municipal government, like St. Petersburg, is where you go when you no longer want to work.

The two men were city roofing inspectors. What they were supposed to do is climb up on the roofs of the city's own buildings and see if everything was okay. If it was, they pressed on to the next building, but if it wasn't they were supposed to summon the city's roofer who, in theory, fixes the roofs.

All this was too complicated for the men. It meant interrupting their schedule of going to lunch, spending time with women, sitting in their (our) truck, watching the passing scene, and going for nice rides in the lovely summertime weather. They had to give up something, so they gave up work.

Who could blame them? In the old days, this was Standard Operating Procedure and when anyone complained that a city worker was not doing any work, the old mayor would yawn and do nothing. The new mayor, Marion Barry, might have his faults, but condoning goofing off on the job is not one of them.

The new mayor, it turns out, read the newspaper account of the work habits of the two roof inspectors, and more or less gave them their pink slips on the spot. Then he called in their agency head, Carroll B. Harvey, acting director of the D.C. Department of General Services, and reprimanded him for what was (or was not) going on in his department. This is the second time Barry has reprimanded a department chief.

Once again, this is a radical departure from the way things used to be done in this town. Department heads are being held responsible for the way their departments operate. The whole concept is downright radical and contradicts the operating principle of all bureaucrats that no one is responsible for anything. I encountered this once when I called the Post Office to complain about some undelivered letters, and was asked by the man who answered the phone, "What do you want us to do about it?"

Now I suppose too much of a case can be made for what the mayor has done. It is not, in the scheme of things, that revolutionary or radical. It is just so sensible that it is stunning. It is, in fact, the second development in as many days to indicate that something may be changing in this country. In New York, for instance, the police are now seizing the portable radios of people who play them too loudly on the streets. It makes your spirits soar.

None of these is a major development. They will not end poverty or educate children or clean up the air, but they do give you a certain feeling that a modicum of common sense had returned to government -- that people will be held responsible for what they do. That some of these people are department heads is the most welcome news of all.

In a way, you have to feel sorry for the two fired employes. On a given day anyone will cheat a bit on the job and even I, stern moralist that I am and lifelong subscriber to the Protestant Ethic, have been known to call in sick when I was merely depressed. But to do absolutely nothing every day a reporter checked shows more than indivudual initiative. It shows an entire support system willing to look the other way, a lack of supervision and a general attitude that the job exists because the job exists -- not because work should be done.

What the mayor has done with the firings is serve notice that this sort of performance will not be tolerated. This is not only good news for the city's taxpayers, but also for the bulk of city workers who perform their jobs well and who are simply mocked by those of their colleagues who prove that work or no work, the pay is the same. Not any more it's not. The revolution's begun.