It was his first night at The Playground Swing Club in Southeast Washington, and the 37-year-old Army veteran was ready. He stripped and headed up the red-carpeted stairs to the lounge where a few men and women, most dressed only in robes, were sitting on cushioned floors and platforms. Sensuous music played in the background as slides flashed on the wall. Soon he and and a young woman he had never before met strolled in to The Playroom, where bodies were lying in all directions on mattressess and a raised platform. w

He and the woman joined in.

"Everybody freeze!" a voice suddenly shouted. "This is a raid!"

The veteran, his new friend and five others, including a man and his wife from Salem, Ohio, are now facing sodomy charges. Dennes Sobin, the founder of The Playground, patterned after other open-sex retreats across the country, and two others are charged with selling alcohol without a license.

The arrests two weekends ago were not your ordinary vice squad busts.

The raid by D.C. police has raised a chorus of charges that they leaned more toward invading the privacy of adults privately doing what they wanted to do than toward enforcing laws to protect the public safety, as D.C. police have claimed they were doing.

The Washington office of the American Civil Liberties Union has offered to defend those arrested, the owner of The Playground says he welcomes the chance to fight archaic morality laws in court and the leader of a local gay right group says he is writing Mayor Marion Barry to protest D.C. police nosing into people's bedroom activities.

"It's beyond me how the government can spend thousands of dollars for police to come in and arrest people for making love," says Eleanor Valentine, who was at the club during the raid but was not arrested because she was talking with friends.

Assistant Police Chief Maurice Turner says The Playground was not raided because of suspected violations of morality laws, but because the place allegedly was selling alcohol, operating as a public hall without a license and violating fire and zoning codes. Police were at The Playground for these reasons, Turner says, and arrested people on sodomy charges only because that, too, is against the law.

"The law is on the books," Turner says, "and we were enforcing it."

Police investigated The Playground for six weeks during which two undercover police stripped to their underwear and spent three hours listening to the friendly discussions and watching the love-making inside the home at 36 N St. SE. Police later kept the house under surveillance for weeks.

"Sexual conduct, between consenting adults," says Arthur B. Spitzer, Washington ACLU legal director, "is none of the government's business."

All of those arrested were adults who had come to The Playground willingly. Some had college degrees and white-collar jobs. An off-duty policeman also was arrested. The people there generally were younger than those who frequent prostitutes, and Sobin has a doctorate in sociology and is the author of three books.

No one arrested at The Playground is charged with paying anyone else for sex. In fact, those arrested, and at least another dozen men and women who weren't arrested, were taking part in a widespread underground phenomenon in America: They were "swinging" -- enjoying sex openly among themselves. What was happening at The Playground was a plain and simple orgy -- an activity that seems to have become as common among a certain underground of adults as was dancing cheek-to-cheek in the 1930s. In fact, some say the Americah sexual revolution has nearly come and gone, that The Playground scene is nearly passe.

No one knows how many people nationwide are swinging these days, although group sex has been included in academic sexual studies as far back as the 1930s and 1940s.

In Washington, the columns of Met Personals, a local swing tabloid, are still full of ads like this one: "Greenbelt, Maryland. Professional couple, trim, white and novice at including others in our sex life, desire to meet similar couples. . . ." And so it goes, ad after ad from Northern Virginia, the District of Columbia and Baltimore. Couples, singles and other combinations seeking to meet in circumstances not unlike The Playground.

Promotion of such get-togethers usually is discreet. Another club, Friends Unlimited in Maryland, has been open for six years. It advertises in Met Personals as "the nation's No. 1 swing club" and takes "couples only." Club officials refuse to discuss what goes on there.

In contrast, Sobin has never been shy about what goes on at his home, The Playground, and that is what led to his arrest. He advertises not only in Met Personals, but even placed a discreet ad for The Playground in the classifieds of The Washington Post on Wednesday, less than a week after the raid:

"Playground Fantasy Players seek additional members for its video workshop series."

Indeed, it was Sobin's announcement of his telephone number on a radio talk show that provoked an outraged citizen to complain to police, after which D.C. police officer called the number himself. That call led to the vice squad investigation and raid.

"It's wasting the taxpayer's money," says the Army veteran whose evening came to a disappointing end after the police raid. "It took police away from more urgent duties. I wonder how many rapes, robberies, burglaries and murders were being reported while they were there . . . Just what harm has the Playground Ten done to society?"

"We call Playground an alternative social club," says Sobin, who also publishes a sex trade newsletter for profit and owns the Red Light, a downtown sex museum. "Many marriages break up because people are looking for sexual variety. This is an alternative."

To be admitted to the club, single women and couples pay a fee ranging from $2 to $80, and that, police say, means Sobin actually is running an unlicensed hall and charging for the wine he serves.

Despite the admission fees, Sobin says the club "is not a business." He insists the payment is a "donation."

Notwithstanding the technicalities of the charges against Sobin, he really has only a single message: "For a married couple in 1981 to be arrested for somomy is ridiculous."

"According to the D.C. statute," says assistant chief Turner, "it's against the law."