The scene: The Center for Alternative Defense, a little-known think tank somewhere outside the Beltway.

The players: KGB agents, CIA agents, Cuban colonels, Pentagon liaison officers, an about-to-be-disgraced senator, his wife and administrative aide, two brothers -- one substituting himself for his brother and killing him.

The situation: By the time the feds came around, a number of people had blown the lid off the potboiler.

Another typical weekend in Washington? Actually, it was a typical made-to-order mystery weekend, this one at the Jefferson Hotel on April 19-21, and everyone -- suspects, victims, the culprit and the paying sleuths -- couldn't have been happier about the whole faked deal, put on by Larry Redmond in conjunction with the Source Theater Company.

What was -- and is -- for real is that mystery thrillers are big business across America: Television shows, books, movies, plays and, more and more frequently, murder-mystery evenings and weekends are cashing in on the phenomenon.

Parker Brothers has come out with a video version of its ever-popular Clue board game (15 million to 20 million sets sold since 1949), and a $10 million movie, also titled "Clue" and featuring all the familiar character/suspects, is due for release around Christmas.

What's not so mysterious, if you listen to Redmond and others in the mystery happening field, are the whys and wherefores.

Says Murder to Go president David Landau, 27: "The last time the United States turned toward mysteries was right after World War II. That was when all the Humphrey Bogart movies were being made, when the pulp novels no longer were considered pulp novels, when we had all the mystery radio shows, everything. And it was that way right after World War I.

"Right now we're basically in the same kind of economic slump . . . a forgotten war, veterans who came back and don't have jobs, unemployment, a basic lack of belief in the system. You read that people get away with anything."

"The mystery's the only place," according to Landau, "where good does triumph over evil, where justice will win out."

"It's a different form of escape," says Redmond, who's forming Partners in Crime here with his wife and two associates. "It combines the idea of a vacation, a getaway, an entertainment -- all in one package. It can be enjoyable for a number of different reasons."

Some people go for the mystery part of it, some for the getaway aspects, and still others, according to Redmond, "try to get behind the game. In both our efforts at the Jefferson, people tried to figure out who the actors were, where they ate at night, who the director was. They tried to get behind the scenes as well as solve the mystery."

The plot thickens:

Paying participants are infiltrated by a group of unidentified actors and actresses playing parts as victims, suspects and the culprit(s) in a mystery plot. Sufficient clues are given so that participants can solve the "crime."

Actors often also take the part of police detectives and other authorities, but they generally leave unraveling of the mystery to the paying guests. Prizes often are given for successful solution of the crime as well as for the most creative solution offered.

At Mohonk Mountain House, whose 1985 mystery weekend was featured in Neiman-Marcus' 1984 Christmas Catalogue, the top prizes are guaranteed (but not free) reservations for the following year's mystery weekend.

"Neiman-Marcus bought 75 rooms," says Faire Hart, program coordinator at the New Paltz, N.Y., resort hotel. "They weren't too sure they'd be able to sell the whole house 150 rooms in winter and spring , since this was the first time they'd offered anything like this."

The Mohonk Mystery Weekend was announced on a network morning television show in September, 1984. Four minutes after the announcement, it was sold out, at $750 per room. When their waiting list reached 1,000, says Hart, N-M called the Mohonk and requested an additional weekend.

Mohonk Mountain House is the old-timer in the business, having put on its first mystery weekend in 1977. Its last several extravaganzas have been custom-written by master mystery novelist Donald E. Westlake.

A Victorian mansion on a mountaintop, the Mohonk is a mystery writer's dream. With stone, wood and turrets, a lake and 7,500 acres of property, it's also popular with mystery aficionados: The single mystery weekend each year has been sold out the day the hotel begins taking reservations.

Participants in recent mystery weekends in the Washington area came from Louisiana, Florida, New York and Delaware as well as the District, Maryland and Northern Virginia.

Redmond and Source Theater already have three mystery events scheduled this and next month -- two one-night mysteries at Meredyth Vineyards in Middleburg, and a three-day weekend at Tysons Westpark Hotel.

"We -- my wife, Kathi, and associates Stephen Hayes and Bill Creed -- do custom scripts, geared to the people and place," says Redmond. The Meredyth mystery involves a number of suspects and likely victims -- a couple of wine critics, a publisher and his adulterous wife, and a wine researcher "who works for the vineyard." Adds Redmond: "If anyone gets killed during the evening, everyone has a motive to do it."

Redmond says his team's specialty is doing things on a large, involved scale. "We have a lot of intramarital and extramarital relationships, social taboos . . . failed business partners, the daughter of a ruined businessman, family revenge . . . a lot of things that smack of 19th-century melodrama that people seem to miss.

"We're trying," says Redmond, "to give them ' "Dynasty" Meets "The Count of Monte Cristo." ' "

Out on the West Coast, Richard Doherr is serving up a different sort of adventure: mystery on a train. Doherr, who describes himself as chief inspector and director of Pickwick Productions and Mystery Train Adventures, says his stories have been set everywhere "from castles to ghost towns," but almost always in- clude a train trip or involve some other formof transportation.

One Doherr-scripted mystery began at a Southern California train station and then ran up the track to San Francisco, where participants began a vineyard-to-vineyard wine-tasting tour in search of Inspector Clouseau, who was being held in a wine vat, drinking "and sinking fast."

Doherr says all his basic adventures start on a train for a couple of reasons: "On the West Coast, everybody uses the freeway. Traveling on a train allows you to become someone else. It breaks your ties with reality."

Everyone, he says, comes in costume. "If they don't, they regret it."

Crime does pay. Prices for Doherr's adventures vary. Day trips, from Los Angeles to another town, run around $90 per person. Birthday trips are $138.

Weekend trips from Los Angeles to Santa Barbara or San Francisco run from $425 to $525, "depending on whether it's a two- or three-day adventure." That fee, says Doherr, includes everything "except drinking, the hangover and return airfare."

The Inspector Clouseau mystery, led by West Coast wine connoisseur Robert Balzer, "ran about $755," including the wine-tastings and roundtrip fare from L.A. to San Francisco and back.

Doherr says he currently is working with a $250,000 budget for a party for a major corporation. "This will involve 18 teams of people, parachutists, boat chases, a double-decker bus . . . " Other Doherr projects involve cruise mysteries -- in the Mediterranean, the Pacific and on the Mississippi River.

Murder to Go's Landau, whose prices for a mystery adventure start at $6,500, claims he was the first to hold mystery adventures aboard trains. "We formed Mystery Express on Pearl Harbor Day, Dec. 7, 1982, but didn't have our first trip until April of 1983." The trip, to run on a private train from Saddlebrook, N.J., to Syracuse, was a disaster, and Landau lost $30,000.

After that, Landau and his partners used Amtrak trains and started turning a profit. Each successful trip was followed by another. Mystery Express evolved into Murder to Go Inc. Today, half of Landau's customers are major corporations.

Landau prices his work accordingly:

* "Mysteries a la Carte," a program for hotels and cruise lines "that don't want to hire us," offers, for $1,500, rights to produce a play, "Murder a la Carte," as well as complete information on how to run a successful mystery weekend, how to get publicity, what films to show, radio programs to play, "a complete package."

* "Murder to Go" rates start at $6,500, plus expenses, for a custom-written mystery for 50 to 100 guests, lasting anywhere from three hours to a full weekend.

* "Murder du Jour," a "specially designed format perfect for corporate functions, conventions and PR events," starts at $8,000 plus expenses, lasts three to six hours and accommodates 100 to 300 guests.

One future Murder to Go production:

* A five-day cruise to Bermuda aboard the Queen Elizabeth II. "It's called 'Murder Overboard,' and we're making fun of mystery vacations." A new game, Murder to Go, developed by Landau and Marvin Silbermintz, a fellow mystery writer and executive at Ideal Toy Co., will be introduced on the cruise.

Meanwhile, back at the Center for Alternative Defense, one thing is certain: The butler didn't do it.