I WAS POOR ONCE. I was very poor and I lived in an apartment with no bathroom, where the toilet was down the hall and where the bathtub was in the kitchen. It had a metal cover over it so you could use it as the kitchen table and when you wanted to take a bath you banged on the cover a couple of times so that the cockroaches would have time to run away. In the winter, it was cold and in the summer it was hot and in the fall I moved out. I was tired of being poor.

I was, in fact, not poor at all. I was living like I was poor, living like so many young people lived at that time. I was pretending to be poor, knowing, of course, that I was not. Being poor is not cheap furniture and a walk-up flat. Being poor is being trapped.

This is something that obviously has not occurred to Mayor Jane Byrne of Chicago who recently moved into her city's notorious Cabrini-Green housing project to see how the other half lives. She chose the place because it is something like the domestic version of Beirut.Almost any night you can hear the sound of gunfire and at last count II persons had been killed and 37 injured in the complex. Police blame the carnage on gang warfare.

So in moves the mayor of Chicago. She gives up her digs high over the posh Gold Coast and says that she will live in Cabrini-Green to find out first hand what life is like there. As an added bonus, the residents of the place get to have the mayor as their neighbor. And since with the mayor comes a small army of policemen and bodyguards and other beefy types out to protect the municipal body, it is likely, but not certain, that for a while at least the killings will abate.

Now you have to admit that what Bryne is doing is in the fine old tradition of politics practiced as theater. John Lindsay, you will remember, ran for president of the United States by sleeping in the homes of the common folk -- sometimes on their common couches. What he got out of the experience, besides a bad back, is anyone's guess. At any rate, the voters were not impressed and Lindsay is not now and never has been president of the United States.

Jimmy Carter followed with his travel bag routine. He carried his own, just like you and me. Just what this was supposed to prove, I cannot tell you since I have been carrying my own travel bag for years and I would be the first to tell you this does not qualify me for the presidency. (I also have slept on more than a few couches in my time.) Carter abandoned his travel bag to walk up Pennsylvania Avenue during his inaugural parade, a move much hailed at the time, but proving, I'm afraid, absolutley nothing.

American politicans are addicted to this sort of nonsense. People run for office by walking for office -- walking across their state, for instance. Bob Graham is governor of Florida today because during the campaign he worked at as many jobs as he could. Of course, he never knew what it felt like to be stuck in one of those jobs, to see nothing in the future but what you saw that day, to work, as lots of people do, day after day at jobs they hate.

Byrne is doing some of that and it would be all right if what came out o it was a plan -- some action. But that is unlikely to happen because you don't have to live in Cabrini-Green to know what is wrong with it and you can't learn what it means to be poor simply by slumming among the poor. Poverty is not something you can dip your little toe into just to see what the temperature of the thing might be.

Byrne is using the people Cabrini-Green, using them to get press and headlines and not noticing, really, that she is patronizing them. Maybe not since American tourists started to go abroad and thought that the poor were quaint ("Martha, ask him if we can pose with his donkey") have we seen so many poor people being used for so poor a purpose.

You have to be careful here. There is something to be said for experiencing things first hand, for doing what we in the journalism biz would call reporting. But to do that, you need not pretend that you are what you are not, that you will live where you know you soon will not. If the mayor wants to give the poor something they almost never get, she could give them some respect. Go home, mayor -- there's real work to be done.