The District of Columbia suffered the highest number of heroin overdose deaths in the city's history last year and nearly doubled the number of cocaine-related deaths compared with 1983, according to D.C. police.

The 138 heroin deaths -- blamed on a flood of cheap and potent heroin -- was double that of 1983, when police listed 69 overdose deaths.

Cocaine was a factor in 88 deaths in 1984, mostly in combination with other drugs, compared with 45 deaths a year earlier. Cocaine-related deaths in 1984 are believed to be a record for the District, said Dr. Rak Kim, acting chief medical examiner.

"It's a gauge of drug activity in the street," said Detective William Larman. "The future doesn't look bright for any reduction. We're going to see a lot more deaths."

Based on records supplied by the medical examiner's office, the narcotics branch of the police department found that heroin and cocaine were found twice as often in bodies tested by the office in 1984 than in 1983.

"It's a multiple drug problem," said Dr. Andrew McBride, commissioner of public health.

"It's really an amazing jump," Kim said of the heroin and cocaine involvement. The records are based on all traces of drugs discovered through autopsies.

The strength of the heroin and cocaine sold in the District also is more deadly, according to toxicology reports. Heroin, which was less than 2 percent pure on the average throughout 1978, was sold in the District last fall in concentrations of 7 percent. Police records show that cocaine available in the District reached a purity of nearly 38 percent. Larman said that a strength of 15 percent is considered average.

Another widely used drug, PCP, continued to contribute to deaths in the District. The synthetic drug was found in the bodies of 69 people who died in the District last year, including two 15-year-old homicide victims. In 1983, there were 65 deaths in which PCP played a part.

Capt. James Nestor, chief of the narcotics branch, explained the increases by saying, "The availability is there. The use of the drugs is up because of the quantities coming in from overseas . . . . Our only hope is to get foreign countries to quit growing the stuff."

Larman said the traditional heroin pipeline, of imported heroin coming to Washington from New York, is eroding in favor of direct importation by Middle East and African immigrants. He said, "They're having mom and dad send it over. Customs and postal authorities know even though arrests are up they're only getting a small percentage."

As is typical of the District's drug usage, the average heroin victim was a black male in his mid-30s. More than half of those who died from heroin overdoses also were drinking alcohol. Police said that since 1979, alcohol increasingly has been a factor in heroin deaths.

"We've been having overdoses in older people, those 50 years and older," said Dr. Robert Reisch, chief of toxicology at the medical examiner's office. "The professional term is 'naive experimenters' who die because the drugs are so strong."

The District's increased drug deaths "are rather discouraging for most of us in this work," said Reisch. "So much money is spent in education, but it doesn't seem to get to the people."

Lonnie Mitchell, director of the D.C. Alcohol and Drug Abuse Administration, said his office holds meetings regularly with the chief judge of the District Court and the medical examiner's office to track the increasing drug usage.

"We have a hell of a problem in the District," he said. "Washington is such an international city, we open ourself up to the heroin and cocaine from out of the country."

Mitchell's agency supports 23 drug treatment centers throughout the city. Another facility, a 61-bed drug detoxification center, is set to open in March at D.C. General Hospital, which also houses a similar alcohol detoxification unit.

"I don't think it increase in deaths means that programs don't work," Mitchell said.

"It's a pattern of increased usage across the country. We're redoubling our efforts, starting health promotion groups in each of the wards. Our goal is to stop the deaths from working down to the younger ages. The older ones, where drug use is so ingrained and hard-core, I don't know if anything can be done."

Nestor said that since the police began antidrug lectures in the schools eight years ago, "not one teen under 18 has overdosed and died on heroin. We take credit for that."

He said his department is beefing up its presentations to stress cocaine and PCP use. "Unfortunately, you've got the cocaine figures, the movie stars, politicians, white-collar types. With that outlook, it's hard to get the message across that cocaine does have addictive powers and that cocaine can kill you."

Drugs also affect the lives of District residents in other ways, authorities say, by being responsible for hundreds of crimes, criminal prosecutions, hospital stays and violence.

Homicide detectives said that 35 of the District's 175 murders last year were attributable to drugs. Another 18 of the 43 unsolved deaths are thought to be drug-related, detectives said.

McBride said the findings may prompt Mayor Marion Barry to give new consideration to the idea of forming a blue-ribbon task force on addiction in place of the separate drug and alcohol groups that currently advise the city.