Deaths and emergency room admissions from heroin overdoses have increased dramatically in the past three years both nationally and in the Washington area, according to federal figures, and many experts say the increases are caused in part by a rise in heroin use by the middle class.

Deaths from heroin overdoses since 1980 have risen 63 percent nationally and 96 percent in the Washington area, the figures show. Heroin-related emergency room admissions have risen 48 percent nationally and 16 percent locally.

In all, there were 11,538 emergency room admissions and 771 deaths nationwide related to heroin use in 1982. In the Washington area, there were 865 heroin-related emergency room admissions and 133 deaths attributed to heroin last year.

"The [heroin] problem is back to the way it was in the 1970s, when it was epidemic," said Dr. Robert L. DuPont, president of the American Council for Drug Education. "What is new is the big increase in the use by middle-class people, which had never happened before."

"There's been a dramatic increase in the past three years in deaths from heroin overdoses," said Dr. James L. Luke, the District's medical examiner until last month. Since the city first began recording the statistics in 1971, he said, there has never been such a high level of deaths.

The federal figures from the National Institute on Drug Abuse also show that since 1975, whites entering programs for treatment of newly acquired heroin habits have exceeded blacks. Although total hospital admissions and deaths from heroin overdoses are not as high nationally as they were in the peak years of 1974 through 1976, they have exceeded those years in the eastern part of the country.

The relationship between heroin usage and deaths and hospitalizations attributable to its use cannnot be firmly established, since overdoses can occur because of changes in the purity of the drug sold to addicts and other factors. The national heroin problem, experts also emphasize, continues to be concentrated among the urban poor.

"What is clear is that there has been an increase in middle-class heroin addicts," says Dr. William Pollin, director of the National Institute on Drug Abuse. In part, he says, that increase can be attributed to those who as teen-agers used marijuana and LSD in the 1970s and have now moved on to heroin. In addition, he said, it has become stylish for cocaine users to level-off the high they achieve from that stimulant with heroin, a depressant.

"I have consulted with a number of physicians, captains of industry and attorneys who use heroin on a very regular basis, even daily. Most got onto it through their use of cocaine," says Dr. Ronald K. Siegel, a psychopharmacologist at the University of California School of Medicine. "It heroin appealed to them as a euphoriant."

Locally, Dr. Tom Stair, assistant director of the Georgetown University Hospital emergency room, says one to two dozen middle-class heroin users come to his center each year with overdoses.

The apparent spread of heroin use was highlighted last month by the arrest and guilty plea of Eric M. Breindel, a staff member of the Senate Select Committee on Intelligence, on charges that he bought $150 of heroin from an undercover police officer in a Holiday Inn in Northeast Washington.

A magna cum laude graduate of Harvard College with a Harvard Law School degree, the 27-year-old Briendel acknowledged to prosecutors he had been taking heroin sporadically since undergraduate days, sources familiar with the case say.

"Some argue our society is falling apart," says Dr. Donald R. Jasinski, scientific director of the Addiction Research Center in Baltimore. "Others will argue we have a youth movement and a breakdown of morality. But people have been taking narcotics in this country for 100 years. The bottom line is nobody knows why people take heroin."

Says a Washington businessman now undergoing heroin treatment at the Psychiatric Institute's Drug Rehabilitation Center in Washington: "You don't say to yourself, 'I am going to be an addict and ruin my life.' It's a gradual thing that starts with snorting, then the needle . . . . I don't know why I did it. It was something else to do."

"The critical thing is it works," says Dupont. "It makes you feel good. The question is, do you cross the threshold to trying it ."

All heroin users do not become immediately addicted, experts say. Some may "chip" the drug for years, taking it just on weekends. Others, however, take it daily and become addicted within a matter of weeks.

Once physically addicted, a person cannot get off the drug without experiencing severe withdrawal symptoms--explosive vomiting, extreme contractions of the intestines, weakness, shaking, sweating, dilation of the pupils and abdominal pain.

What many people do not realize, DuPont says, is that addicts often continue to function in their jobs for some time before any impact becomes evident. "Once a skill is acquired, it is amazing how long it can go before the heroin has an effect," he says. "Other things--personal relationships, for example--will fall apart first. It could go on for years."

For the casual and addicted user alike, heroin is an expensive diversion. A bag, or "quarter" of heroin--named for the quarter of a teaspoon it equals--costs about $35 to $40 in Washington and $100 to $200 in Virginia. Each bag is good for one shot, and a typical drug addict takes from one to four shots a day.

Says a 31-year-old Washington area banker trying to get off a $150-a-day habit at the Psychiatric Institute, "I did it just for the kicks."