Plentiful and potent heroin from the poppy fields of Iran, Afghanistan and Pakistan is killing people in the District of Columbia at a greater rate than ever before.

Eight persons have died from apparent heroin overdoses in the city in the last five days. The latest deaths brought to 50 the number of persons who have died of drug overdoses here in the last three months. Since the first of the year, 72 overdose fatalities have been recorded compared with 62 in all of 1980.

D.C. Police Chief Maurice Turner called the deaths an epidemic and said the sharp rise in heroin use is "causing the crime rate to soar." In addition to the overdose deaths, there have been about a dozen heroin-related slayings this year, according to police officials.

The record year for overdose deaths was 1971 when 82 deaths were recorded.

Police and health officials yesterday blamed the dramatic rise in deaths this year on the purity of heroin on Washington's streets, saying it is now up to 6 percent pure compared with levels of about half that normally.

Joseph Savoy, head of the city's drug treatment program, said competition to sell heroin has been so fierce that earlier this year many new dealers trying to crack the market were giving away free samples. "That's unheard of," he said.

D.C. police said that although one victim, a Silver Spring man, was only 25, most of the latest overdose victims were in their 30s. The oldest was 37. The age of the addicts was another indication that the heroin being pushed is more potent than addicts are used to buying, police said.

"That's some dynamite stuff," Savoy said. Instead of staying away from the more powerful heroin, addicts are seeking it out, he said. "The addict population is a strange one," he said, adding that "a few deaths" will actually promote a new dealer rather than scare away new customers.

The incidence of overdose deaths here always rises sharply whenever a purer strain of heroin hits the streets, one veteran narcotics investigator said.

"An addict develops a tolerance for the amount of whatever grade of heroin he's been buying. Then, when he tries to adjust his dosage for the better stuff, he just miscalculates.

"More often," the investigator said, "the addict is simply unaware of the greater potency of the new heroin. If you're used to shooting two, three percent stuff, and all of a sudden you're getting a double dose, there's no doubt about the result."

Heroin, a morphine derivative, is a powerful depressant that acts on the central nervous system, and injection of two large a dose can bring about death through shutdown of one or more of the body's involuntary vital functions, such as respiration or heart action.

Police Capt. James P. Nester, head of the narcotics enforcement office, said all the victims were found with either used syringes or other heroin addiction materials, but that the offical causes of deaths will be determined by toxicology reports due in a few days. Nester said there was no indication of other causes of death.

Police said the death of the Silver Spring man, who was found Sunday in his car in the 900 block of Rhode Island Avenue NW, was another indication that suburbanites are traveling to the District to purchase hard drugs. The man apparently was suffering from withdrawal pains and pulled over to inject himself, according to police officials who found heroin paraphernalia in the car.

The other deaths, the most recorded in any one weekend period, included two women and four men, all of whom lived in the District, and one man who is still listed as a "John Doe."

On Monday night, police responding to a report that two men and a woman were "shooting up" in an alley behind the 1300 block of U Street NW, found the body of a 37-year-old meat cutter on the front steps of 1347 T St. NW.

A woman who had been in the alley with him was found unconscious and taken to George Washington University Hospital where doctors saved her life. The third person, a man, could not be found.

Also Monday night, a 34-year-old roofer and building insulator was found by a relative in an apartment in the 500 block of Foxhall Place SE. Police said the man was taken to Greater Southeast Community Hospital where he was dead on arrival. The man's family told police the victim was a veteran of Vietnam and had told them he began using heroin while there.

On Saturday, police said, the father of a 34-year-old woman found his daughter's body slumped in the bedroom of their home in the unit block of W Street NW.

Police said the father reported that he had seen his daughter 10 minutes earlier sitting on her bed. He told police his daughter had used heroin before but he believed she had broken her habit.

Three victims were found on Friday in separate incidents. The body of a 34-year-old woman was discovered on her bathroom floor in the 2200 block of Champlain Street NW. A syringe with traces of blood was found on the floor next to her, along with a belt that police said was used to help inject the herion.

A 31-year-old man's body was found in a room at the Hawthorne Hotel, 2134 G St. NW, when police were called to the hotel to investiage a foul order. The man, who apparently had been dead a couple of days, checked into the hotel July 24, according to police. A syringe was found next to him.

The third victim on Friday was a 34-year-old man whose body was found in an apartment in the 600 block of Rhode Island Avenue NW.Police said the body was found after a call by another man who said he had been "oiling up" with him.

Last Thursday, the body of a 30-year-old man was found in a basement hallway at 1236 11th St. NW after a tenant reported three men using drugs in the building hallway.