On the front page of our Metro section yesterday, there appeared a story about Mayor Marion Barry. It was written by Writers Eugene Robinson and Keith B. Richburg.

The thrust of the article was that although Barry was once considered a friend of unionized workers and was elected with strong union support, he has recently been the subject of labor's jeers rather than cheers.

While Barry was building his political base, he was for more jobs and higher pay. Unions representing policemen, firefighters, schoolteachers and others worked hard for him.

But now that he's mayor, Barry has been cutting the District government's work force and trying to hold down pay increases. Needless to say, those affected by these attempts to balance the budget are angry with him.

Robinson and Richburg quoted Joslyn Williams, head of the political arm of the Central Labor Council, who said: "When (Barry) was a council member, he argued for parity between D.C. workers and federal employees. He sees things differently now, (but) we don't know what caused him to change."

Permit me to offer a guess as to why he changed: Barry is no longer one of the outs trying to get in. He's one of the ins trying to stay in. He is using an incumbent's ultimate weapon: the courage to face reality and accept the responsibility for making unpopular decisions.

If you're thinking about going into politics, everything you need to know can be covered in two easy lessons.

Lesson 1 -- When you run against an incumbent, blame him for everything that goes wrong anywhere in the solar system, regardless of whether the incumbent had anything to do with it or whether George Washington himself could have handled it better.

If Iraq attacks Iran, blame the incumbent (and try not to look embarrassed when the ayatollah climbs into bed with you and also blames the incumbent).

Make extravagant promises to every special interest group. Whatever the incumbent does, or proposes to do, attack him fiercely and imply you could handle the matter much better; but don't volunteer too many details as to how you'd do it.

Lesson 2 -- If you win office, don't waste your time defending yourself against all the people who would like to oust you so that they can get your job. If you respond to their attacks you just help generate publicity for them. The best way to get yourself reelected, or to win a higher position, is to conduct yourself in a responsible manner in the job you have. Once you realize that you can't please everybody, it's easier to concentrate on figuring out what's best for everybody, regardless of who will be pleased or displeased.

Running for mayor and serving as mayor are very different -- as different as a 15-year-old child who is in rebellion against parental restrictions and a 40-year-old parent who recalls all too well why those restrictions are necessary. If Joslyn Williams will keep in mind that we are dealing now with Marion Barry the mature man, not with Marion Barry the young firebrand, there will be no great mystery about what has caused his outlook and his priorities to change.

The District of Columbia is not at the brink of bankruptcy, as New York City was a few years ago, and Barry knows that it is his reponsibility to see that we don't reach that point. He must act in what he deems to be the best interest of all the people -- and then he must be man enough to take the abuse that is sure to be directed against him by critics who judge public policy by their own self-interest. REBUTTAL

A few days ago, a local resident complained about the recent increase in professional licensing fees. For good measure, he said the District government offices with which he dealt seemed overstaffed and inefficient.

Kathleen S. Williams of the city administrator's office informs me: "Fees have been raised to cover the cost of issueing licenses, which is considered a resonable move in these days of budget shortfalls. Procedures are being revised to speed up licensing procedures and to make the process more convenient for applicants."

She adds this comment about employee eficiency: "While one can always point to some employee who appears to be working less than he or she ought to be, I personally know one employee of that office who puts in two or three hours extra every day just because she feels a strong sense of responsibility about her job.

"Increasing employee efficiency and productivity has been a major focus of Mayor Barry's administration, and a series of changes are being made to bring this about."

Barry's efforts have been supported here. I think most of my readers are hoping he succeeds in straightening out the mess he inherited.

The others may be planning to run against him next time.