The advertisement read: "WANTED: 12-YEAR-OLD MILLIONAIRE who will appreciate this incredible 'fun house' in McLean, Va.

"So far," said Joyce Baseman, the real-estate agent, "we've had some millionaires call and some 12-year-olds, but nobody who's both."

To call it a "fun house" is absolutely accurate. A fun-house distorting mirror is even part of the equipment. Other distractions include: an interior basketball court, an exterior platform tennis court, a whirlpool big enough for the whole team, two saunas, 7 1/2 bathrooms, intercom, wine cellar, four-car garage, 300-gallon gasoline tank, four fireplaces, servants' suite, various strategically placed ceiling mirrors, a trapdoor, a secret bedroom, secret beds, a round bedbase, several other variations on beds, trunk lines for 50 phones, four heating systems, two security programs and three conversation pits.

All this is in a 11,000-square-foot classic contemporary house of cedar, glass, masonry and elaborate landscaping, set on an acre of land in McLean.

So far, said Baseman of Golubin & Warwick Realtors, most of those interested in the house have been bachelors. Though if the zoning permitted, it would ideal for a health club, a coeducational executive retreat, a splendid place for an orgy, or, as it was planned to be, a home for a family with grandiose ideas, six children and a husband who worked at home.

The house was designed by architect Ronald L. Molen and built six years ago by James Dyer, then head of Research Homes, as "the forever home" for his wife Renie and their children. Unfortunately, forever isn't that long these days. After a series of complicated legal problems and financial reverses, the Dyers left their home and this area. But they obviously had a magnificant six years in the house, amid every plaything a child could imagine and more than most adults could buy.

The current owner hired a management firm headed by William Fitzgerald -- Menequil -- to hire Golubin & Warwick Realtors to sell the house. It's been on the market since February, first for $795,000, now for $785,000, cheap at twice the price. Baseman said the house cost $650,000 to build, but that would have been the builder's bargain. It surely would cost twice that to build, now.

On the other hand, as Baseman admitted, "it would take a particular type of person to want to buy it." Not to say one who could afford to clean all that wall-to-wall carpet.

The gee-whiz effect begins when you come into the arrival court on the meandering driveway, past islands of planting and modern Japanese lanterns illuminating enough parking space to manage quite a party. The zig-zag steps, made of congrete aggregate framed with wood, are like a ceremonial entrance to a monument. The steps lead up through a huge masonry foundation wall into an entry court formed by the house's U shape. A trellis extends from one wing to the other. The planting is carefully organized. The grandiosity of the house is immediately announced by the three elaborate front doors. Each has raised wood panels affixed to the door. A door in one wing leads to the family quarters, two doors on the other side go to the servant's apartment and the office and recreational area. Attached to one is a carving of the word "office" and a carving of a house.

We took the conservative route, into the family side. The two-story front hall has a curving balcony and a staircase. Wall-to-wall cream-colored carpeting spreads like spilled milk all over the house, frequently covering several built-in banquettes.

The living room and dining room are adjacent. They're not such large rooms but interestingly laid out. A two-story high area with a window big enough to see the world is at one end of the room, where you'd expect people to stand at a lartge party. The ceiling here is elaborately painted with much wood trim.All through the house, walls are framed with dark stained wood, and wood is used as an accent. The other part of the room is divided into two sections. A step-down inglenook has built-in banquettes by the fireplace. The dining area has a wall of built-in storage with drawers lined in Pacific cloth for silver. In Dyer's day, it had a round table with an inlaid Lazy Susan "designed to get people together at one of the times when they talk most . . . while eating," Dyer once wrote.

The adjacent kitchen had, as well as elaborate swing-around canned-good storage, a bult-in rolltop desk, a dumb waiter from the garage and the usual ovens and cooking units.

The big room in the family quarters is adjacent to the kitchen. It's sort of a Great Hall, where the family gathers (with clean feet, one would hope, considering the amount of pale ivory carpet). A two-story high section looks up at the bedroom-level balcony hall. A sunken sitting area has built in banquettes facing the fire. Baseman said that when the family was in the house, the children came down by a fireman's pole. One wall is cedar, painted white.

The library with bookcases and a carpeted window seat offers a haven from the more public Great Hall.

For adults who are not up to the fireman's pole, the stairs lead to the second level. The children's room are just above, full of the extensive carpentry and carpeting that cover the house. The bedrooms for the younger children have ladders to the upper level, that would have been the attic. The children can climb up from their bedrooms and down into the hall. The beds are built above head level with room for a secret study area below. A room for an older child has a carpeted frame for a mattress. Another bedroom has double bunk beds.

The master bedroom suite has a carpeted circular base for a round mattress, bolstered against a built in curving headboard with controls for lights, television and the security system. Around the corner is a sybaritic sitting area with a curving carpeted banquette facing the fireplace. Built-in bookcase fill another wall.

Two separate dressing rooms with compartmented storage and built-in drawers, large bath with bidet and sauna complete the master suite.

The most remarkable side of the house is the office complex and the recreation area. Not recreation room, you understand, but AREA. Even that's too small a word. The principal room is a 78-by-25-foot, three-story high interior basketball court and gym. A 30-foot rope for climbing hangs in the middle and goes up to an aerie on the top. The super-size Jacuzzi big enough for a whole basketball team is under the balcony. The weights system is elaborate.

The swimming-pool-sized pit under a trampoline is lined with red, white and blue carpeting. A sauna with dressing room and lockers, showers and a bathroom are conveniently located. A trapdoor and a ladder lead to a hidden bedroom and both under the basketball court. A huge glass window wall lightens the whole effect.

Just in case you're still raring to go, the immense platform tennis court with an umpire's box, staircase, swings and heaven knows what else stretches across the back yard.

The office suites are on the same side of the house as the recreation area. You come into the reception room, and you wonder just what you're being received into. Blood red carpet covers the floors and a dais for the desk. Above is a large mirror, affixed to the celling. In the next room, a larger one, the windows are frosted glass. Another window looks into the gym. The second office has a cathedral ceiling with an elaborate lighting system built into it.

The conference room is the real surprise. Another of the ubiquitous banquettes takes up most of the room. A suspended ceiling above the conference table supports lights underneath, a mattress on top (if the meeting gets too dull?). The conference table itself is built onto a dental chair base, so it can be lowered or raised.

Bookcases and a giant light for reading architectural plans are on the other side of the room.

As Dyer put it in a description he once wrote of the house: "An increasing number of important business transactions occur on the court or in the sauna . . . businessmen are realizing that creative and innovative business decisions often do not fit into a sterile square corporate office."

The servant's quarters are not second-class. The living room has a fireplace and a gallery kitchen. The bedroom has a built-in platform for the mattress.

A walk-in food storage room (the Dyers are Mormons and believe in keeping a year's supply of foodstuffs), wine cellar, workshop, furnace room and four-car garage are also tucked onto this level.

Like any house with nobody living in it, this one has an eerie feeling. It is such a personal house that visiting it without its owners makes you feel as though you are walking through some one else's dream. The secret nooks and crannies give it a wonderland quality, as though any moment you might tumble down the rabbit hole or see Humpty Dumpty who couldn't be put back together again. We tended to talk softly so the lares and penates of the house would not know we were there. We look over our shoulders to see if something did dart behind the door.

Today, the house has an expectant air to it. The whirlpool whirls away with no one to feel its waves. The rope from the aerie in the gym sways seductively. The ceiling mirrors reflect only emptiness. The conversation pits echo only silence. The tennis courts and swings stand quiet and forlorn in the bright June sun. The first game is over, the players have left the field. Who will call the next round? And how will they play the games?