After a sharp decline in recent years, the quality and availability of heroin appears to be on the rise in the streets of Washington, according to D.C. police.

They say the crowds of youths who congregate to buy and sell heroin have become larger and bolder in the last few months, particularly along 14th Street NW, which still is the center of drug activity.

A recent rise in violent crime appears to be related to this growing drug traffic, police said. The bodies of at least three addicts, wrapped in blankets or carpets, have been found in vacant houses and alleys in the 14th Street area during the last three months.

Mayor Marion Barry directed police last week to wage "all out war" on drug traffic along 14th Street after receiving numerous complaints from the nearby Logan Circle Civil Association and businessmen on 14th Street.

City police have stationed a sergeant, six uniformed policemen and several plain-clothes vice squad detectives to one three-block area of 14th Street just to disrupt heroin traffice there.

According to police, a record 150 drug-related arrests were made in a two-block radius from 14th and S streets NW between Feb. 21 and May 20. But, these apprehensions put scarcely a dent in the burgeoning drug activity, according to police officials. They say they expect to double the number of arrests in coming months.

"There is an increase in forcible robberies and a jump in aggravated assaults - even a couple of homicides - that we have reason to believe are all tied into the distribution of drugs in that area," said William Dixon, deputy chief of the 3rd District, which has responsibility for the 14th Street area."We are going to approach this problem like we used to do with prostitutes. We're going after the customers. If we can make it harder for them to make a buy, they'll soon stop coming."

More than $50,000 worth of drugs have been confiscated on 14th Street this year compared to about $30,000 during the same period last year, police sources estimated.

These same sources said they believe that more than $120,000 worth of drugs are sold each day on 14th Street between T and Q streets NW.

The quality of the heroin sold is improving; the price for it is declining, police said.

Although not as conspicuous as on 14th Street NW, drug use in other known "drug centers" appears to be on the increase also, with heroin, Preludin and marijuana heading the list of abused drugs. But police make more narcotics arrests in the 14th Street area than all other areas of the city combined.

"Fourteenth Street is to narcotics what Vienna is to SALT talks," said one policeman. "People from all over town come here to deal."

During much of the past year, the average $70 bag of heroin was about 1.3 percent pure, police said. Recently confiscated heroin has been determined to be about 4.6 per cent pure, police said. At the same time, the price for a bag of heroin has dropped to about $50, police said.

Authorities suspect a variety of factors have contributed to the apparent rise in heroin use. When several area druggist and doctors were indicted last year in a scheme to sell a weight control pill called Preludin - known on the streets as "Bam," - the product became "hot" and street dealers shyed away from it. Deprived of the Preludin, which generally sold for around $3 a hit, some drug users turned to the more expensive heroin.

Police began a preliminary offensive against drug sellers and purchasers on 14th Street on Friday by arresting and ticketing persons congregating on the streets on charges such as loitering, jaywalking, double parking and violation of the antilitter laws.

"There are some people hanging out there who don't live around here. Basically, we're going to make them go home," said Capt. Richard Gurz, head of the 3rd District's police vice squad. "We're going to eliminate this problem using every tool we have. Specifically, our objective is to change their habits."

There has been a see-saw battle between police and drug pushers on 14th Street for more than 15 years. The last major effort was in October 1976. Maurice J. Cullinane, who was police chief then, declared that he was "getting tired of seeing those people hanging around there." He issued orders to "clean up 14th Street."

A few months later, Charles Rinaldi, then deputy chief for the 3rd District, conceded that make the problem go away. "It's like a balloon," Rinaldi said. "If you squeeze one area, another pops us. And as soon as you let up on enforcement, they come back."

The 3rd District's new deputy chief, William Dixon, said he was optimistic that the new offensive would rid the area of the drug problem "once and for all."