SOMEWHERE IN THE CITY of Washington, an eight-year-old boy shoots up on heroin. He does it every day. The needle is administered by his mother's boyfriend who is, in effect, the boy's guardian. No one stops this from happening. In Washington, the family that shoots up together can apparently stay together.

The kid's story was reported Sunday in The Washington Post by Janet Cooke who heard about the boy from someone and then simply asked around. She did not conduct a six-month undercover investigation. She did not pose as a junkie. She did what anyone could have done. She asked some questions, followed her nose and, in due course, found the boy.

Cooke promise anonymity. She promised no police.She promised to write her story and nothing else. This is the sort of deal reporteers have to make from time to time.It's an imperfect arrangement, but at least now we all know about the boy. It's up to others to do something about him.

During the interview, the boy talked about his heroin habit. He talked about how he loved the stuff, how he saw nothing wrong in using it and someday -- knock on wood -- dealing it. He had already picked up the underworld ethos that there is no choice in this life but to steal and deal and wheel. Already at eight he believed there were no jobs and no hope and no opportunity. Later, when he was starting to come down from his high and get withdrawal symptoms, his "father" grabbed him, put a needle into his arm and shot him up.

The boy went calm again. People came into the house to buy their drugs. When Cooke finally got to her car, she threw up.

I come from a part of town where the eight-year-olds don't shoot up. I come from a place where when the kids in the third grade started trouble in Spanish class, the principal had the teacher call the parents and, later that week, the incident wad discussed withthe gravity normally attached to a prison riot. Between the parents and the teachers and the principal, it was a sure thing that the incident would not repeat itself.

But I know that life can be different across town. I know that there are places in the city where the teachers would settle for a little insurrection in the Spanish class and where is a parent expressed an interest in the school the teacher would fall over and faint. I know this. President Carter is not the only one who knows that life is not fair.

But I do not know how a kid can go to school high on drugs and the teacher does not know it. I do not know how he could come down in class, go into withdrawal, and the teacher or the principal or someone does not notice. I do not know how an eight-year-old can be a junkie and the school does not know and the teacher does not know and someone does not go to the house with an ax and ask for some answers.

I do not know how a eight-year-old can be a truant all the time and no one seems to care. I do not know how that can be. I do not know how the schools can not care or can not afford to care or don't have enough people to care or don't have the right people to care. How can this be, and if it can be -- and it obviously can -- then how can we be talking of cutting the school budget? This is not a story of frills. This is a story about a kid dying.

I do not know either how a reporter can find her way to an eight-year-old who is an addict but the police do not know. How is this possible? How is it possible that the drug enforcement people with their trillions of dollars in federal aid and their computers and their police officers did not know of this kid -- could not do what a reporter could do? How is it possible when people are streaming in and out of the house, buying drugs, when they are shooting up in the place, when the man of the house is a dealer and the lady of the house is an addict, dealer and former hooker? She is also the boy's mother.

Somewhere in all this is a story of failure -- of massive failure. Somewhere in all this is a story of agencies not caring or not doing their jobs, of money being spent on the wrong things, of schools not paying attention, of well-meaning but defeated teachers who cannot cope and, also, maybe just as important, neighbors who knew or suspected and didn't do a thing. Somewhere in all this are a lot of questions that the city, the school system and the mayor ought to answer. An eight-year-old boy is about to die. Somebody, for crying out loud, ought to care.