He was the cop on the beat, and his beat ran from 7th Street to Connecticut Avenue, across the needle-scarred depths of street- corner drugs at 14th and U. He would lean on the addicts when officials downtown got hot about swarms of junkies on the streets.

Then it all turned around. The cop became the junkie, with a desperate need for heroin that ate up over $100 a day.

The man who got the habit was not only the law at 14th and U for five years but also the son of a successful city businessman. He still lives with his parents on the exclusive Gold Coast. He was the son who had all the clothes, the records, the son who was sent to college, the football player, the little prince of his family. He became the junkie.

"Damn, he was a good cop," says Larry Melton, now an official of the International Brotherhood of Police Officers. "He was never one to get along with authority. You know, he was with the group that got out of high school in the '60s and came on the force at the start of the '70s. I think he wore a shoulder bag. That generation didn't do things because you told them to do it. They'd ask why ... but he was a good cop. There was no problem with him covering my behind parts."

Why anyone becomes a heroin addict, or even gets involved with heroin, is open to argument. But the spiraling number of addicts is shown by the record number--94--who are already known to have died from heroin overdoses this year. That surpasses the previous record of 82 reported heroin deaths in 1971, when the city was said to have been in the grips of a heroin epidemic. The dead, as well as the others hanging onto life at the end of a needle in the current wave of addiction, include more than poor people, the unemployed and the uneducated. Counselors at city clinics say that more and more of the addicts are working-class people, if not middle-class people who have some education, and they live everywhere--in the suburbs, in the best city neighborhoods--and hold good jobs.

Dr. Kurt Brandt, acting medical director of the city's Alcohol and Drug Treatment Services Administration, says the rate of admissions at his clinic for people who have never used heroin before has risen 30 percent in the last year. The reason for the increased number, he says, is the increased availability of heroin.

"With so much heroin available," Brandt says, "it is now crossing social lines like never before. . . . Let's say you've never tried cocaine, and you are at a party. A good friend says, 'Try this.' You've got a lower threshold than if someone came up to you on the street and said, 'Try some cocaine.' It is like that with heroin. Heroin has been getting into the social scene with professional people now because it is so plentiful and there is not the fear of heroin that there used to be. People who have tried marijuana and cocaine have gone past some psychological barrier of fear of drugs. If they run into heroin in the right situation, they are going to try it."

In the policeman's case, the heroin led to dismissal from the police force after five years on the beat. The good cop was doing heroin two or three times a week. It had started as a weekend habit in the Army. He had smoked marijuana and snorted cocaine in college, before being thrown out after two years. But in the Army, it was heroin. And soon after he came back to Washington, it was heroin again. Even so, the police department did not know he was shooting up; he was put off the force for constantly being late for roll call and out sick for days without a medical excuse.

"The officers never liked me," he says. "I'd talk back to them. When I started messing up, it just gave them the chance to get me." He is sitting in his parents' home, feet up on a glass and chrome coffee table with copies of Ebony and Life set just so at either end. A chubby man, about 6-foot-3, he is still doing heroin but fighting to stop. Walter Gilmore, a counselor at the Georgia Avenue Veterans Outpatient Hospital, confirms that he has been a patient since July.

"I started messing up real bad in '75," he says. "Up to then I was making money, carrying the gun, being a policeman. I was a big man. Then I was 25 in 1975, and that's when all hell broke loose. I was always telling myself I'd be a lawyer or a doctor, that I would go back to school. Suddenly, I was 25, and I knew I'd never be more than a cop. Me. I was always going to do big things. I mean, people expected it of me. If my cousin showed up at a dance with Raquel Welch, I was supposed to show up with the Dallas Cowgirls."

Still, this addict is a very special case because he was a cop walking through the bizarre, swarming circus of hard drugs, and yet he bought the drug package for himself.

"I always looked down on those people (the addicts on 14th Street) as low-life, filth," he says. "For me it was an experiment. I figured I could handle it. I could cut it off when I was ready. It didn't have me. I had it.

"I couldn't handle it. Turns out it handled me."

In the clutches of heroin, he became a bad cop. He wrote fictitious parking tickets and phony reports on suspicious persons to make it look as though he was working. To get money for drugs after he was put off the force, he pulled con games, like charging several insurance companies for phony accidents. He prided himself on not breaking into houses or mugging people to get money for drugs.

"All heroin addicts aren't standing on the street, you know," he says with a sarcastic laugh. "I know heroin addicts who work every day, people from a far higher economic strata than myself. It's a shame that one of Robert Kennedy's sons was involved with it. It's a shame that John Phillips (of the Mamas and Papas) was doing it.

"Why do they do it? I'll tell you, man, when I'm high, all the pressure is off. I don't see my parents asking why I'm not a lawyer. I don't feel my own disgust with what I've done. Nothing matters but the feeling."

Even when he had been thrown off the police force and his car had been repossessed, his parents never guessed he was doing heroin. "A mother doesn't want to see that," he says. But slowly it all came out, especially when he took a little too much in an S Street shooting gallery last August and had to be rushed to Howard University Hospital to be revived. Still, it is a family secret. It might hurt his father's business if the word got out. He asks to go unnamed as the ground rule for talking with a reporter.

But he wants his story told. He hopes it will make a good script for a movie. Until then, he wants to get into TV or radio broadcasting. He's looking for that big break, that big job that will carry him to another high--stardom. Sad.