With little governmental opposition and apparently strong consumer demand, Washington has become a wide-open city for a mushrooming, increasingly aggressive retail sex industry.

From a few relatively tame adult bookstores, strip clubs and girlie movie houses concentrated in a small downtown area, the business has blossomed into a much larger phenomenon and spread to quiet residential neighborhoods and suburban shopping centers.

At the same time, the nature of goods and services sold in today's sex emporiums has rendered outdated the old definitions of soft and hard-core pornography. Some examples:

About 50 adult bookstores now operate in the District of Columbia and its suburbs. Close to 30 of them are inside the Washington limits and offer a wide mixture of books, films, magazines and "rubber goods." Subject matter ranges from what one Baltimore distributor described as "clean" - explicit depictions of straight or homosexual sex - to the extremes of sadomasochism, bestiality, child pornography and other fetishes.

A similar number of sexually oriented massage parlors, most of which operate as legally untouched brothels, flourish in the city and suburbs with the District again containing the majority. Simultaneously, about a dozen "outcall massage" services provide sex for sale to hotel transients who need only pick up the phone to secure a radio-dispatched prostitute.

More than 40 D.C. establishments, by police count, now feature nude dancing in almost all sections of the city. In some places, dancers also engage in simulated or actual sexual acts with customers as part of their performance or perform later in darkened booths for extra money or in return for the purchase of grossly overpriced champagne. No "bottomless" bars are known to operate in the suburbs.

The expansion of the sex industry into the suburbs, which started about three years ago, has been slowed by what its owners consider harrassment by local officials. That crackdown, although uneven, has resulted in a back-to-the-city movement in search of a less hostile business climate.

Contributing to the current situation are D.C. court decisions, expanding what is permissible in Washington; juries reluctant to render guilty verdicts in obscenity cases, and judges who seldom impose harsh penalties on persons convicted of such crimes.

Police and prosecutors, frustrated by a permissive legal climate and concerned also with more violent crimes, have in turn placed a lower priority on these so-called "victimless crimes." On top of all that, the City Council in 1976 abolished the police department's prostitution, perversion and obscenity squad.

Then, the City Council, heavily lobbied by owners and civil libertarians, refused to enact the same type of stringent regulations for massage parlors that exist in the suburbs. The District's 1932 law against "cross-sexual" massages, rarely enforced, is now under legal attack.

Other cities, notably Baltimore, have used a bawdy house law to close down such operations. A similar law is on the books here but has been seldom used.

Massage parlor operators generally deny any responsibility for prostitution that occurs on the premises, but many of them acknowledge that it exists and is, indeed, widespread.

Many of the parlors have well-appointed interiors, elegant beds rather than massage tables, stereophonic music, and in some cases, movies. Some also provide "torture" rooms for the masochistically inclined.

The businesses are staffed largely by a mobile work force of young women, and frequent turnover is common.

A different group of women, often with long ties to one employer, staff the District's bottomless bars and nightclubs, both as waitresses and dancers.

These establishments vary in clientele and performances and start with the few remaining topless luncheon places patronized by businessman. In some, nude dancers engage the customers in close sexual encounters.

Then there are the producers of pornography, largely in Southern California, and the increasingly sophisticated merchandisers. Some of them own or control movies, massage parlors and book stores, and both wholesale and retail goods and services.

It's big business, by all accounts, often producing profits well into the millions for the largest companies.

Baltimore's Bon-Jya Sales, the largest provider of pornography for the Washington market, according to police and industry sources, has successfully diversified. Names of persons associated with Bon-Jay have turned up as operators of at least five downtown book stores, one homosexual movie house and a massage parlor in downtown Washington.

Washington contains one wholesale warehouse, Atlantic Magazine Co. at 3748 10th St. NE, which is associated with Donald Epstein, whose 9th Street NW bookstores offer what police say is a generally softer brand of pornography than the others.

Locally, the sellers of pornography are a small closely knit group, many of them proteges of Herman Lynn Womack. Womack, a rotund, former philosophy professor now living in Norfolk, once owned 10 stores in Maryland, Virginia and the District. He was barred by the terms of his probation in a 1971 obscenity case from further participation in the business.

Owners of sex-oriented establishments frequently hide behind "straws," often $150-a-week employees whose names are used to comply with legal requirements that someone's name appear on applications and permits.

Acting as a straw has frequently sent employees to court on criminal charges of selling abscene material.In at least one instance, it has caused a hapless employee financial ruin. One woman once employed by Womack's Village Books, and now selling real estate on Capitol Hill, found herself liable for $9,150 in rent on one store and $61,379 on a note she had co-signed to cover material from a California distributor. Faced with no alternative, she filed her bankruptcy in 1975.

Despite the ebb and flow of court decisions, Washington police keep close watch on the bookstores and arrest employees where material purchased by undercover police is deemed sufficiently "obscene" to persuade at least one judge to sign an arrest warrant.

To the extent they are able, the pornography merchants have been fighting back. Through their lawyer, Stanley Dietz, they filed two lawsuits last fall to enjoin what they said was undue harrassment by the city. Both were dismissed in D.C. Superior Court.

In book and magazine sales alone, the largest Washington stores are said to gross up to $1,000 daily, at markups of 100 per cent, and often much more.

According to former bookstore employees, some owners use various devices to hide their true incomes. "When I sold films," said one employee, "none of the money went into the cash register; it was put in a separate bag." Another man said his boss kept two sets of books, one for himself, which was destroyed daily, and another for his auditor and Internal Revenue.

Peep show machines are especially lucrative and have increased in number here from 200 two or three years ago to 700 now. Owners are required to register the machines and pay an annual D.C. fee of $30 per machine, compared to $300 in Baltimore.

Quarters fed into the film machines buy two- and three-minute segments of film, often requiring $5 to $7 to complete the entire hour-long reel.

One Washington shop with about two dozen machines grosses between $1,200 and $1,800 a week from them, according to a former employee. The owner, the employee said, disconnected the machine counters to hide his earnings and eventually had users buy slugs to avoid theft of coin boxes.

Anyone with $5 and the time can also view a full-length adult movie in a Washington theater. In explicitness they are at least the equal of "Deep Throat," yesterday's X-rated chic classic and one of the few films to be held obscene here. Movie prosecutions continue but with no certain expectation that convictions will result.

In the Washington area, "adult movies" are also available from rental outlets, along with the cassette machines needed to view them. The list of movies available from one Silver Spring outlet, along with alltime Hollywood classics, include "Bordello," "Prurient Interest" and "1,000 Danish Delights." X-rated films rent for $10 for two days, tape players for $35.

Under a 1973 U.S. Supreme Court decision intended, in Chief Justice Warren E. Burger's words, to "isolate 'hard-core' pornography" from constitutional protection, what's legally obscene is supposed to be determined by local standards.

While the courts struggle to define "obscenity" here and elsewhere, countervailing political pressures have begun to build here.

Congress is expected early this year to adopt a tough law against the sale and distribution of child pornography, a practice even strong civil libertarians have difficulty defending.

There has also been increased resistance from neighborhood groups in Washington who want to protect the values of their children and their property from the threat they perceive in nearby pornography bookshops and massage parlors. Officials have responded at least to the point of expressing new concern over the proliferation of pornography and forming task forces.

At the same time, the D.C. Zoning Commission has extended its ban on new "sex-oriented" business in certain areas. The ban has no impact, however, on bottomless bars or on established businesses. And in at least one case, a new massage parlor declared itself "not sexually oriented" on its occupancy permit application, there by skirting the law.

"People interested in erotics have rights, too," protested Al Goldstein, publisher of Screw magazine, to 90 sober-faced lawyers at a recent American Bar Association conference on obscenity and the law. "The sexual customer has to be protected, too."

The widespread acceptance of such an attitude, both official and otherwise, has encouraged the growth of the sex business in Washington.