Nine fatal overdoses last weekend furnished stark new evidence of heroin's increasingly deadly hold on Washington.

The District is a major center of the heroin trade, law enforcement officials and experts on drug abuse say.

Washington's death rate from overdoses is far out of proportion to the city's size. In the year that ended Sept. 30, according to federal government figures, there were 185 heroin overdose deaths in the Washington area, in contrast to much larger metropolitan areas, such as Chicago with 53, Detroit with 91 and Philadelphia with 65.

The heroin traffic here is distinctive not only for its volume but also for its openness. D.C. police have identified 20 locations throughout the city where heroin is bought and sold openly on the streets. Four are major 24-hour-a-day markets, serving as virtual convenience stores for the city's estimated 12,500 addicts.

Often addicts and "chippers" -- casual recreational users -- pay to shoot up in "oil joints," shabby basement or first-floor apartments near the marketplaces. For those too frightened to inject the drugs themselves, there are "hit doctors" who will do the job for $5.

Mayor Marion Barry, Police Chief Maurice T. Turner and other city officials years ago declared "war" on heroin in Washington, and they have been issuing new declarations ever since. But they also have spoken often of the frustrations of battle against a global drug trade. "Heroin," Barry has often said, "doesn't grow at 14th and T."

Police stage periodic raids on the more flagrant heroin depots, disrupting business for a time. But in the long run they succeed mainly in pushing the dealers from one street corner to another, or dispersing them more widely throughout the city.

"We realize that we can't stop it," said Capt. James Nestor, head of the D.C. Narcotics Task Force. "The best we can do is try to put a hurting on the people who use it. Our job is to make the citizens happy. Citizens don't like seeing addicts congregating on the streets, so we keep chasing them around the city."

Despite the efforts of police and city officials, the death rate from overdoses keeps rising -- in 1980 there were 82 in Washington, a high number compared to other cities but less than half as many as last year.

One contributing factor in the rise of the heroin death rate in Washington is the increasing purity of the drug sold on the city's streets.

Inspector Kris Coligan, head of the D.C. police department's morals division, which handles narcotics offenses, said that in 1978, heroin seized on the streets averaged 1.8 percent purity -- that is, it contained 1.8 percent pure heroin. By last year, he said, the average had risen to 6.2 percent; now officers are seizing heroin of 7 percent purity.

So the police chase the addicts and the addicts chase the drugs. And on the evening of March 1, as people all around the city began dropping from overdoses of an untraced batch of lethally potent heroin, Assistant Police Chief Isaac Fulwood went on the 11 o'clock news to warn users to stay away from narcotics that night.

The city government had assumed the role of consumer watchdog.

What police are up against in the fight against drugs in this city is quite different from what they are battling in other major urban areas. Police say that instead of organized crime controlling drug trafficking, as in New York or Chicago, Washington's drug business is controlled by makeshift clusters of addict-dealers -- a hierarchy of friends and acquaintances who operate as crime captains, lieutenants, sergeants and crew members.

Police and other sources give this account of how these drug organizations work: A captain sets the tone for his operation with the name he chooses for his product -- "Direct Hit," "B-52," "Cujo," "Black Tape," "Rattlesnake," "J.R." or "Murder One," just to name a few of the scores of brand names that identify not just the drug but also the people associated with the operation.

While crew members work the street corners in eight-hour shifts, sergeants determine what kind of stolen goods will be accepted in lieu of money. Lieutenants tally the proceeds and make sure that the city's "dope centers" are supplied at the right time of the month.

The drug business is regulated by the day of the month, with the 1st, 3rd and 15th being the days when the "best" dope is put out on the street to lure new customers. These are the days when welfare and other government benefit checks are received, and drug dealers are known to offer discounts to welfare mothers in an effort to get them hooked.

By the end of the month, when money is tight, a type of drug dealer known as the "garbage man" takes over the market, selling an "inferior quality" drug at prices as high as the market will bear.

Using a mixture of substances such as iron, quinine and confectioner's sugar to increase the quantity of the drugs, the garbage man is often as dangerous as the dealer who puts out a purer product.

"Last weekend will happen again," said Coligan, referring to the overdose deaths. "They drug dealers are not chemists or doctors. These are street people. They are not mixing this stuff in a lab. They make mistakes and errors, and they will end up killing people."

"It's a hellacious cycle," said Alfred McMaster, a D.C. narcotics detective who recently dressed up in a Schlitz Malt Liquor Bull costume and lured heroin buyers into one of this city's most spectacular drug stings. "You have low-income kids coming out of one-parent households who look at drug dealers and think that they are somebody. And the kids want to be somebody.

"They go home and ask mom for $10, but mom is on welfare and $10 is a lot -- like dinner for a family of six. So mom says no. But the kid knows how he can make some money, and be somebody, too."

While the makeshift crime associations are more conspicuous, police say there is another group involved in the trade -- perhaps three or four major heroin dealers who are second- and third-generation pushers. They do not use heroin themselves, and they try to avoid contact with addicts, whom they consider beneath them.

The National Institute on Drug Abuse compiled a statistical portrait of heroin users in Washington, based on 1983 and 1984 data from hospitals, the medical examiner's office and the U.S. Department of Health and Human Services.

Seventy-two percent of the city's heroin users are addicts, the study found. Twenty-two percent use the drug for "psychic effect," which seems to reflect what authorities say is an increase in casual or weekend use of the drug. One percent had used heroin in a suicide attempt.

Half the city's heroin users, according to the profile, are between the ages of 20 and 29. Another 40 percent are in their thirties. Three-quarters of Washington's heroin users are black; two-thirds are male.

The study found that the vast majority of users -- more than 96 percent -- take the drug by injection. Less than 1 percent take heroin by smoking, sniffing or swallowing it.

Dr. Lonnie Mitchell, head of the D.C. government's drug abuse programs, said the city estimates that there are 12,500 heroin addicts in Washington. He said the city's drug treatment programs see a monthly average of 3,400 persons.

He said city officials recently decided that methadone maintenance programs -- in which the heroin addict is given methadone, which also is addictive -- are not a workable long-range solution.

"We have people who have been on methadone for 12 or 13 years," he said. "In November we made a decision to limit methadone to two years." He said the city is starting to use another substitute drug that is not addictive.

The openness of the heroin trade here is striking. "The street markets are the fastest way to sell the stuff," police Capt. Nestor said. "It is unreasonable to expect us to eliminate drugs in the city without elimination of the supply. No enforcement agency could eliminate the drug users without stopping the supply. If the supply stopped, you won't need us there."

Nestor added, "The only thing that bothers people is what they can see. No one would care if it were indoors. That was the case with cocaine. It was sold indoors for years, and now that it's on the street, people care about it."

The heroin problem has been primarily confined to the city, but D.C. police homicide detective Ronald Taylor recently held a heroin seminar for police officials from Prince George's, Arlington, Fairfax, Fauquier and Charles counties. The session focused on such things as discerning evidence at the scene of an overdose death and how to read an addict's "historic tracks" -- the needle marks in his or her arm that give a clue to the victim's background.

"They are just starting to see the problem," Taylor said. "And some of these guys thought syringes were only used to shoot insulin."

Assistant Police Chief Ronal Cox, who has jurisdiction over the morals division, said police have not given up on attempts to stop the heroin traffic and the related crime it generates as addicts steal to maintain their habits. "We don't want to contain it," he said, "we want to eliminate it."

Cox added, "We are hoping to get some major traffickers off the street and make the situation unbearable. . . . If you don't do anything about it, then you are giving a license to people to traffick in drugs.

"When we get to the point where we accept defeat, we have lost. . . . I have to believe that we will win. We can't tolerate what we have got.. . . We can't let discouragement beat us."

Heroin, former users say, seems to hold you in its warm arms and protect you from the cruelties of the world.

The line between being a "chipper," or casual user, and being a junkie is a fine one. Those who have crossed it say it might be the step of injecting the drug instead of sniffing it. Or it might be the point at which the need for heroin is not to enjoy the intoxication, but to cover the pain of heroin's absence.

Sharon and Paul, two residents of R.A.P. Inc., a private nonprofit drug-treatment center on Willard Street NW, spoke last week about how they came to embrace heroin and how they have struggled to free themselves. Both asked that their last names not be used.

Sharon, 34, seems the picture of the young professional woman. She is educated and articulate, and she dresses with the panache of the upwardly mobile. She says she used heroin for 16 years.

"I was a chipper from 1968 until 1979," she said. "In '79 I started injecting heroin because I had blown out my nose and ears."

She explained that the substances that are used to cut heroin damage the user's nasal membranes, and that she also got ear infections from sniffing drugs. "I just couldn't inhale any more. Snorters delude themselves about not having a problem."

From 1979 until last year, Sharon said, she used heroin daily.

"I was able to go to work," she said. "I was productive. I kept getting raises until the very end. There is a myth that you have to be on the street level and act like a derelict to be a junkie. That just isn't true."

She said she used to buy her daily heroin at 14th and W streets NW, Washington's best-known heroin market, on lunch breaks from her office job.

"I paid my dues on 14th Street," she said ruefully. "I got burned sold bad dope because I was a well-dressed female. They used to say to me, 'Show me your track marks,' because they thought I was a cop.

"I used to shoot up in the car. A single woman doesn't attract attention sitting in a car alone. I'd pull up to a stoplight, have my leg all strapped up, and cook it up and shoot it before the light changed. No one would notice."

Paul, also 34, said he was attracted by the excitement of the life style. "The risk-taking was one of the lures," he said. "There is an element of excitement of going downtown and buying drugs on 14th Street. I chose to go there because I liked the cat-and-mouse thing with the police."

Sharon and Paul both described their visits to "oil joints" or "shooting galleries." Using heroin is an expensive proposition: About $35 to $40 to buy a teaspoon's worth of heroin, called a "quarter" on the street; $2 to enter the "oil joint"; $1 to buy a syringe; and another $5 if the user wants someone else to inject the heroin for them.

The "oil joints" or "oil houses" are generally furnished with old couches and chairs and other furniture, and they sometimes have mirrors positioned high on the walls so that a user can see to inject his or her neck.

"You have a certain posture when you approach an oil joint," Sharon said. "You are ready to shoot, and you don't want no crap from nobody."

Paul added, "You knock on the door and someone always says, 'Who's there?' And you say, 'Man, open the door!' You get a little impatient."

It takes only a few pieces of equipment to prepare the heroin for injection: a syringe, a bottle cap, a cigarette filter and a match.

The user puts the heroin and a bit of water into the bottle cap, heats the mixture until it dissolves, and then draws the mixture into the syringe through the cigarette filter, which traps some of the impurities.

The user then injects the heroin, or has someone else perform the injection.

Sharon and Paul complained that Pepsi-Cola and Coca-Cola bottle caps have gotten thinner over the years, and tiny holes sometimes appear in the caps when they are heated.

"You watch it drip out," Paul said, "and you die."