Overdose deaths among Washington heroin addicts, a key barometer of heroin availability on the streets, increased dramatically last year, totaling 62 in 1980 compared to 41 in 1979, police reported yesterday.

Police said the 1980 statistics also showed that the average age of city addicts in now about 32 years -- compared to the early 20s five years ago -- and that many are combining use of alcohol and other drugs in large quantities with heroin.

The increase in deaths began more than a year ago with the influx of Iranian and other Middle Eastern, or Golden Crescent, heroin, officials said. In the past, most heroin coming into the District of Columbia has been impure, brown Mexican heroin or white heroin from the poppy fields of Southeast Asia.

More recently, the influx of the pure, Golden Crescent variety has proved dangerous to addicts used to using larger quantity of less potent heroin.

The study, compiled by detectives from the narcotics division of the D.C. police department and by the District Medical Examiner's Office, showed that:

The majority of those who overdosed, 47 of the 62, were black males.

Of the deaths, 52 had a prior history of drug use, according to police, hospital and court records.

The largest number of those who overdosed lived in far Anacostia.

Forty-three of the victims were found to have alcohol in their systems, and 27 had one tenth of 1 percent or more alcohol in their bloodstreams, indication of legal intoxication.

D.C. narcotics inspector Chris Coligan said yesterday that the higher death rate can be attributed partially to an addict population in the city "that is into 'poly' drug abuse, mixing several drugs with heroin, mostly alcohol and Preludin."

The greater age of the victims, he said, indicates "that some of the addicts who went off heroin when it was hard to get a couple of years ago turned to alcohol and now that heroin is more available they're back on heroin and mixing the two."

"Occasionally," he said "the drug dealers, in preparing heroin for street use, lose track of how they're cutting [diluting] the heroin and they'll end up with a street bag of unusually high purity. For instance, we have seized one bag of heroin for street sales which was 80 percent pure, another around 28 percent. The average heroin on the street is about 4 percent.

"When these potent drugs are shot up by an addict who's used to 4 percent, he's going to overdose," Coligan said.