If you can't afford to buy a Nelson Rockefeller house, a Rockefeller antique or even a Rockefeller reproduction, at least you might be able to scrape up $5 to visit the former Rockefeller estate at 2500 Foxhall Rd. NW.

The mansion is this year's Decorators' Show House, a benefit of the Women's Committee for the National Symphony Orchestra. After invitational previews, the house will be open, beginning Tuesday, from 10 a.m. to 3:30 p.m. weekdays and from 12:30 to 6:30 p.m. Sundays, through Oct. 23.

All the furnishings, chosen and installed by 32 designers, are for sale. But if you can't afford to buy anything, there are a number of excellent decorating ideas offered free. And there's the pleasure in seeing how the great and near-great lived.

You come into the property by an entrance so hidden that most people miss it the first time. The long winding drive through tall trees, azaleas and rhododendrons gives you a feeling of really going somewhere. The 25-acre estate was one of the largest privately owned properties in Washington, almost a tiny principality itself.

Unfortunately, the principal residence is a building that consists of a 1791 farmhouse and a 1932 mansion uncomfortably joined in a U shape. The courtyard looks out over a pond. A swimming pool and a tennis court are terraced down from the house. Happy Rockefeller once said that the pool was a great relief to her husband Nelson after a hard day at world affairs.

Rozansky & Kay, developers of the entire 25-acre estate, are offering the house and some land for $750,000. Architect Arthur Cotton Moore is designing new houses in the $350,000 range for the rest of the estate. The Foxhall Road neighbors first bitterly protested development of the estate, but an agreement as to the density and access has been reached with the neighborhood.

Rockefeller bought the house in 1946. He and other members of the family used it during their periodic government service and for political entertainment. He and his wife lived in the house while he was vice president, though they redecorated the official Vice President's Residence.

Before the symphony's designers started work, the house looked rather sad and neglected, as though no one cared very much for it. It had rather the air of a camping place or a pied-a-terre , though the Rockefellers' art and antiques would have made a great difference.

When the symphony women's committe came to look at the house, they saw the bomb shelter under the foyer completely equipped with the emergency food rations, a tank of water and power generator. All have been removed, perhaps to another safe haven.

The proper attitude for viewing a home of the mighty is induced right away as you come in the door and see the busts of two Roman emperors on pedestals in the foyer. Bob Waldron Interiors painted the walls a pale blue to set off the crystal chandelier.

The designers were asked by the symphony committee to use a comfortable country style in the farmhouse el and a more sophiscated urban attitude in the later part of the house.

The library - designed by Lord & Taylor's Gail Jackson assisted by Carol Herman - carries out their theme of the sport of kings. There are polo-players sculptures, a horse painting an even a horse fireplace screen.As a relief, there's a wood deer from China roasting atop the radiator. As in most of the rooms of the house, the rug is an Oriental. The walls are a wonderful Chinese red with a red-flowered fabric on the comfortable sofa and chairs.

It doesn't have to be a big room to be clever, points out Barbara Campbell of the Persimmon Tree in Potomac. She took on what was a little hall between the older and the newer sections of the house. The two poorly designed closets each are hardly big enough for Happy Rockefeller's fur coat. Campbell turned them into a useful and pleasant cloakroom The walls are papered with a river scene. The bamboo coat rack stands near a carved country bench where a rag doll luxuriates.Two china cats are warming themselves on the radiator, and a mirror with a carved wind face overlooks the two closets, which have lost their doors and become alcoves for a desk and a chest.

Sarah Eveleth decorated the country living room with a table and desk on the upper level and a bench and wooden chairs on the lower level. With great sense, she left the French doors bare to look at the pond.

The cheerful family supper room, by S.D. Jeffery Associates, was probably the farmhouse living room. It has a pleasant fireplace. If the library is a horse room, this one has gone to the dogs. There are dogs in a painting above the settee, porcelain dogs on the table, Fu dogs in the window, china dogs in the cabinet and even a smug-looking porcelain dog in a brass dog bed with cushion by the fire. In an alcove is a banquette covered with a flowered fabric, matched by the valance, and two drum tables topped with glass, for the supper.

Frank Angel, the landscape architect who cleaned the pond for the benefit, made a pleasant sleeping porch on the upper level, using a straw mat to hide the bed springs.

Gayle Yotheimer's country bedroom has a Shaker peg board on the wall. A stenciled wallpaper strip goes all the way around the top of the wall. The bed is set across a corner. A dead tree limb, sprayed white, fills in the triangle. The room is fully equipped, including a chamber pot set in a woodcase.

Woodard Ltd, with the Tile Gallery did the adjacent bath, with a hand-painted flowered sink.

In this section of the house, the ceilings and walls are a dreadful composition board, surprising to find in a Rockefeller house, but the designers have covered up rather well with paint and mirrors. The teen-ager's bedroom by Marjorie Mitchell and Dorothea Lindemere has sunk beds and a cheerful attitude.

One of the best-looking rooms in the house is Susanne Shaw's guest bedroom. Shaw started with a dhurrie rug of a pronounced pink pattern. She had a screen made of hollow doors, hinged together (not expensive ro difficult to do) with the pattern from the rug painted on it by Lucy Morrison. A Plexiglas chair by Russell Williams, another one of the sparkling Jeffery Bigelow console tables and a Plexiglas table that started out in life as a bench add glitter to the room. Shaw had the yellow wallpaper and fabric made by Zina in Port Chester, N.Y. Around the fireplace is a plastic laminate made to look like stainless steel. Shaw says it doesn't clean all that well.

Christian Zimmer of Abacus made a dramatic bath next door with a mirrored coffered ceiling and deep brown tiles. A small mirrored vitrine is especially nice.

Designaire's bedroom is obviously for a crown princess, with a fanciful canopy in an embroidered fabric (economy-minded souls might try it with mosquito netting). The fabric also is used for a set of screens that substitute neatly for curtains - today's best idea.

An adjacent bath by Margot Wilson is festooned with a hand-painted, fabric-canopied ceiling. In the boy's bedroom by Edward Richardson Associates the bed is built into a storage alcove.

The room by Keith Babcok and Associates is tiny but big enough for a wonderful British folding bed/chair circa 1850 and hhe Crimean War.

Designers Choice imported a magnificent bed and armoire in the Napoleon III style of ebony wood. The 1635 painting is of William Shelly. The walls are military gray. Against all this 19th-century look is the modern classic Eero Saarinen champagne table, a small version with a black marble top used as a night table. Also from Knoll International is the Hannah settee, here in a red plush to blend with the period pieces.

Design Factory's Fran Wallinford turned out what may be one of the town's cleverer dressing rooms. The closet wall, doors and in between are covered with 1920s ladies in hats and other regalia painted by Edith Murray. Bright idea: It's all painted on Pellon, applied with an iron and coated with wax. Removable. The room also is ornamented with a stained-glass window, which also has a '20s fashion theme by Sunburst of Fredricksburg's Thurmond Radford, and fans, combs, perfume bottles and hatpins of the period.

Jules Rist of Oakton/Leesburg designed the rather palatial master bedroom with a canopied bed and pleasant chairs at the fire.

One of the neater views is down the circular staircase and a peek at a skirted table and a marvelous clock, all by Town & Country.

Other rooms will be decorated by Woodward & Lothrop, Hecht's, Burklew Design Associates, George Bulger, Kerry Touchette, Dennis Cory Interiors, Dennis Tile Sales, Carolynda Campbell and Roush Averill.

For information on tickets, directions and parking, call the Decorators' Showhouse 333-4473 or 333-9698.